[preproman]

  Verdict (IMO, in case someone needed a cheap disclaimer):
HE-4>HE-500>>>HE-400
 
For my music tastes, I prefer the spaciousness and aggression of the HE-4 over the musicality of the HE-500. I tend to listen to a lot of instrumental stuff, so vocals have never been something I long for. The HE-400 is still one of my "least" 

 favorite headphones, it just can't compete against its brethren.

 
Great review man.  The way you have them rated with the categories you used I agree with you 100%.  Female vocals on the HE-500s are to die for.  The instrument separation, air and imaging on the HE-4 are great.  The HE-4 has the best air and space I've heard in the Hifiman headphones.  Not to be confused with width and depth of soundstage.
 
While I have no experience with the Project Ember I'm wondering would the HE-6, HE-5LE or the HE-5 be a good match.  As you go up in amps you will see how the HE-6 scales and separates it self from the pack, also the HE-5 and HE-5LE to a lesser level.  
 
I like where you said the HE-500 and the HE-4s treble can go either way and the HE-400s treble is terrible (I said that).  IMO the HE-4s treble extends more and has a better sparkle compared to the HE-500.  The HE-4s can sound a tab bit bright depending on the DAC, but it's pretty true all the time.  Unlike the HE-400s the treble can be all over the place.  
 
I've found the HE-400s have a classic U shape with a mid rage suck out, while the HE-500 has a slight mid range hump.  The others are pretty even with slight treble increases on some with some amps.

 

[Thujone]

Great review man.  The way you have them rated with the categories you used I agree with you 100%.  Female vocals on the HE-500s are to die for.  The instrument separation, air and imaging on the HE-4 are great.  The HE-4 has the best air and space I've heard in the Hifiman headphones.  Not to be confused with width and depth of soundstage.

While I have no experience with the Project Ember I'm wondering would the HE-6, HE-5LE or the HE-5 be a good match.  As you go up in amps you will see how the HE-6 scales and separates it self from the pack, also the HE-5 and HE-5LE to a lesser level.  

I like where you said the HE-500 and the HE-4s treble can go either way and the HE-400s treble is terrible (I said that).  IMO the HE-4s treble extends more and has a better sparkle compared to the HE-500.  The HE-4s can sound a tab bit bright depending on the DAC, but it's pretty true all the time.  Unlike the HE-400s the treble can be all over the place.  

I've found the HE-400s have a classic U shape with a mid rage suck out, while the HE-500 has a slight mid range hump.  The others are pretty even with slight treble increases on some with some amps.

Thanks a lot! Regarding Project Ember, I've read several positive results with the HE-6. The Garage1217 website states that it can power the HE-6 as well as the K1000, but I have seen a other users confirm that. Your mini review (which is where I got this review style from ) makes me very curious about the HE-6. The level of diminishing returns is already too high with the HE-500, so I am hesitant.

As far as the HE-400 goes... It's just plain odd. Something you'll love or something you'll hate!

 

[preproman]

The level of diminishing returns is already too high with the HE-500, so I am hesitant.
 

 
That's the thing with the HE-6.  It will send you down a rabbit hole fast with no end in site.  Diminishing returns plays a big part in that.

 

[koiloco]

Thanks a lot! Regarding Project Ember, I've read several positive results with the HE-6. The Garage1217 website states that it can power the HE-6 as well as the K1000, but I have seen a other users confirm that. Your mini review (which is where I got this review style from

) makes me very curious about the HE-6. The level of diminishing returns is already too high with the HE-500, so I am hesitant.

As far as the HE-400 goes... It's just plain odd. Something you'll love or something you'll hate!

Even though pricing is often relatively subjective based on each individual.  Keeping the prices of all flagships in mind, I personally don't think HE500's level of diminishing return is high at all.  Actually, I found it to be a very good deal comparing to other flagships I've listened to including the HE6, HD800.
About Ember powering HE6, you really should take that with a grain of salt cuz if you think HE500 takes a bit of pwr to bring out what they could offer, HE-6 will need even more.  People might be ok with the SQ from their HE-6 driven by Ember but IMO, that's underpowering that HPs.  With HE500, the ember will be fine based on specs.

 

[Soundsgoodtome]

   
About Ember powering HE6, you really should take that with a grain of salt cuz if you think HE500 takes a bit of pwr to bring out what they could offer, HE-6 will need even more.  People might be ok with the SQ from their HE-6 driven by Ember but IMO, that's underpowering that HPs.  With HE500, the ember will be fine based on specs.

What kind of power should the HE6s be taking? The HE-4, to my understanding, takes even more to power properly than the 500 but less the HE6, correct?

 

[koiloco]

  What kind of power should the HE6s be taking? The HE-4, to my understanding, takes even more to power properly than the 500 but less the HE6, correct?

This could be a little subjective and not easy to verify the point at which one can say that the HE-6 is being fed enough pwr.  My WA22 puts out 1.5w+ and drives my HE500 fine but it doesn't give the HE500 the same "thump" across the board as my Emotiva Mini-X (around 10w at the HE500's impedance).  When I listened to HE-6 on a Schiit Mjolnir (5-8w), I felt that the HE-6 was given adequate power.  On the Emotiva Mini-x, there was no difference/improvement I could hear vs. the Mjolnir so I would venture to guess that around 5w should be a good starting point.  That happens to be the power output of Hifiman EF-6 too,  5w @ 50 Ohms.

 

[Thujone]

Even though pricing is often relatively subjective based on each individual.  Keeping the prices of all flagships in mind, I personally don't think HE500's level of diminishing return is high at all.  Actually, I found it to be a very good deal comparing to other flagships I've listened to including the HE6, HD800.
About Ember powering HE6, you really should take that with a grain of salt cuz if you think HE500 takes a bit of pwr to bring out what they could offer, HE-6 will need even more.  People might be ok with the SQ from their HE-6 driven by Ember but IMO, that's underpowering that HPs.  With HE500, the ember will be fine based on specs.

So you've listened to the HE-6 on Ember?

 

[beianfanla]

While the word "polite" may have  negative connotation associated with it, I think that "musical", "intimate", and "full" are more positive words to describe them. As for the HE-400 and HE-4 pairing, I think that's a good pair for sure! In fact, it's probably a better pairing than the HE-4 and HE-500 since the HE-400 is so much different.

 

[koiloco]

So you've listened to the HE-6 on Ember?

I haven't had the chance therefore what I said was purely based on a stronger amp and a weaker amp.  Ember has about the same power as my Woo WA22.  The specs on the Ember looks great and should be decent for HE500 though it doesn't have as much pwr as say Schiit Lyr that has great proven synergy with HE500 and enough pwr to spare.

 

[Thujone]

I haven't had the chance therefore what I said was purely based on a stronger amp and a weaker amp.  Ember has about the same power as my Woo WA22.  The specs on the Ember looks great and should be decent for HE500 though it doesn't have as much pwr as say Schiit Lyr that has great proven synergy with HE500 and enough pwr to spare.

You shouldn't base an amps ability to power headphones purely based on their power output. Some users would say the Lyr struggles with the HE-4, yet it has a much higher output power than Ember. Power isn't everything. I don't understand it myself, but the Magni has about equal output power as Ember at the low impedance yet it struggles greatly with the HE-4. As many have said, you can't judge equipment you haven't listened to. Maybe someone who knows more about amps can educate us both on this matter, all I know is what I've heard.

 

[koiloco]

You shouldn't base an amps ability to power headphones purely based on their power output. The Lyr is known to not have the ability to power the HE-6 and many have said that it struggles with the HE-4, yet it has a much higher output power than Ember. Power isn't everything. I don't understand it myself, but the Magni has about equal output power as Ember at the low impedance yet it struggles greatly with the HE-4. As many have said, you can't judge equipment you haven't listened to. Maybe someone who knows more about amps can educate us both on this matter, all I know is what I've heard.

While I agree with some of your points,  assuming that manufacturers are accurate/honest about their output rating, there's nothing magical or unknown about whether an amp can drive a pair of HPs properly, though properly is somewhat a subjective term depending on who you ask.   As I said, Lyr is known to be able to drive HE500 well cuz this is a well known/popular combo.  Lyr/HE6 is a lot rarer and less known so I didn't speculate on that.  Also, No, magni doesn't have as much pwr as Ember.  On top of that, it's reverse, for magni, it's 1.2watt at 32 Ohms and goes down to 1w at 50 ohms and down further as impedance goes up.  The Ember is somewhat opposite until 120 Ohms(1, 1.5, 1.8 in an increasing manner till 120 Ohms)  So at around 50 Ohms, the Ember does have around 1.5x more pwr than Magni.
Anyway, as I said, your hearing is very subjective and it's hard to argue and make a point from that.  I don't have a problem driving my HE500 with my Fiio E17 on high gain and ok with the SQ.  But at the same, I have a little monster Emotiva Mini-x who feed 10wpc into the HE500 so I know exactly what I am missing on the E17.  You might be fine with what you have and what you hear until you hear something better and can distinguish the difference.  I was a big skeptic of more power bull schiit when it came to ortho HPs like HE500, HE6.  I bought the Emotiva just to verify and prove those advocates wrong but it turned out that I was the one who didn't know better and was wrong. 
Until you have experience the same journey, let's leave it as that.  
Last of all, I am not dissing Ember in anyway because it's a product I haven't had the luck to try personally.  My suggestion and input have always based on what I know and the gear I have experience.  The rest is specs which should be pretty black and white.

 

[Thujone]

For the impedance we are talking about, Magni and Ember output nearly the same amount of power... How come when I increase the output impedance of the amp, to have a much lower output power than Magni, the Ember still shines? This is a problem of manufacturers being dishonest? I would love to have this concept explained to me. In the past, whenever I've asked similar questions, the most popular response is "power isn't everything". While I don't care for that answer, I have no grounds to argue with it.

 

[laizhaomade]

While the word "polite" may have  negative connotation associated with it, I think that "musical", "intimate", and "full" are more positive words to describe them. As for the HE-400 and HE-4 pairing, I think that's a good pair for sure! In fact, it's probably a better pairing than the HE-4 and HE-500 since the HE-400 is so much different.

 

[Modular]

For the impedance we are talking about, Magni and Ember output nearly the same amount of power... How come when I increase the output impedance of the amp, to have a much lower output power than Magni, the Ember still shines? This is a problem of manufacturers being dishonest? I would love to have this concept explained to me. In the past, whenever I've asked similar questions, the most popular response is "power isn't everything". While I don't care for that answer, I have no grounds to argue with it.

I think it comes down to the type of power. Let me explain:

We'll start with a simple equation.
P=IV
P is wattage, I is current (measured in amps), and V is voltage. Let's say that the HE-4 needs 2 watts to sound "good". According to this equation, there's more than one way to get to 2 watts. You can either increase voltage or increase current.

Increasing voltage is generally pretty easy for most electronics, supplying the proper current, however is another story. If the amp isn't actually strong enough to supply the necessary current, then the signal will get distorted and sound lifeless.

The same can happen with the voltage. If the circuitry cannot keep the voltage stable then a drop in current will result.

This is an oversimplification of the issue as there are many other factors as resistance in headphones (and all speakers for that matter) changes with the frequency as well, but hopefully it helps explain why a quality amplifier matters. Maybe someone with more knowledge can chime in as well.

Also, many manufacturers may use the simple V=IR equation to figure power. Where V= Voltsge supplied, I = Current (measured in amps) and R = Resistance of the headphones. This isn't going to result in real world power output, but figurative numbers instead. This is likely why budget amps claiming high numbers don't sound good on phones that need stable current and voltage.

 

[Soundsgoodtome]

^^ Makes sense. This is why Bottlehead sells the Speedball upgrade for the Crack then. It doesn't change the power output but is able to keep up with the power demand, or somewhere along those lines.

Also, when a manuf states the wattage an amp is putting out, it's safe to think that they're putting PEAK power and not RMS. I've only seen 1 headphone amp state RMS on their power rating, I forget which.