[benbenkr]

Some headphones are not affected by impedance mismatch. But till a point, yes the HD558/598 doesn't sound that nice directly out of the SBZ.
One may feel that the extra bloat in bass is actually a good thing for the rather bass shy HD558/598, but problem is that when the mid-bass hits hard then distortion occurs. Not ear-tearing distortions obviously, but enough to annoy IMO.
 
On the other hand, the 32ohm Fidelio X1 doesn't suffer any distortion but made a lot of the details way too bloaty. Mids were quite blanketed.
Again, some people may like it as it gives the illusion of a deeper bass presentation but I personally don't. I like my bass clean and refined, with energy and impact.
 
One last thing (though it isn't a huge issue), adding an external amp through the headphone out of the SBZ means double amping. So if you are going that route, make sure to get an amp with as low as possible on THD and as clean as a signal accross the frequency range.

 

[Solarium]

This impedance mismatch thing with the HD598's kind of steers me into getting a Asus Xonar instead. Anyone know if they also have the impedance mismatch with the HD598's. Also will the Xonar's CMSS-3D software emulation sound as good as Creative's hardware version? I'm also assuming that the Xonar's can drive the 50 ohm headphones without any issues correct?

 

[DJINFERNO806]

From what I remember the xonar stx has a 10 ohm output impedance, same as zxr.

Dgx has about a 10 ohm output according to most people on here.

And the dsx and dx have about a 100 ohm output impedance apparently.

Asus cards aren't going to make it better if your worried about impedance mismatch.

 

[Solarium]

I know it's kind of out of my price range, but how does the Xonar STX compare to the SBZ? I like the idea of having both the headphone output as well as the line-out so I don't have unplug my headphones every time I want to listen to my speakers. But the idea of EAX 5.0 software emulation bothers me and I'm not sure if it supports a lot of recent games given its 2009 release date.
 
Also, I heard somewhere that the Titanium HD has better sound quality than SBZ. Anyone can comment on this?

 

[benbenkr]

Asus Xonar's Audio GDX thingy which simulates EAX doesn't.... work. At least, it never did for me since I was using the Uni Xonar drivers. The stock official Asus drivers were just too unstable to even care about using anything.
 
As for virtual surround, Dolby Headphones is fine... I like it as much as SBX. I can freely switch between the both anytime and wouldn't have an issue with it.
 
Anyways yeah, going to a Xonar STX isn't going to help with the impedance mismatching either though it certainly wouldn't be as bad. I had a HD558 connected directly to a FiiO E09k previously which also had 10ohm output impedance (which actually has the same headphone amp as the Xonar STX) and it wasn't bad. For one, there weren't distortions and although the bass did feel a little uncontrolled, it at least didn't cloud the mids of my HD558.

 

[PurpleAngel]

This impedance mismatch thing with the HD598's kind of steers me into getting a Asus Xonar instead. Anyone know if they also have the impedance mismatch with the HD598's. Also will the Xonar's CMSS-3D software emulation sound as good as Creative's hardware version? I'm also assuming that the Xonar's can drive the 50 ohm headphones without any issues correct?

Looking at getting the Asus Xonar Essence STX?
You could get the Asus Xonar DX or D1 (used $60) and the Schiit Magni headphone amplifier (new $99).
The Magni has a headphone output impedance of less then 1-Ohm
So you can plug the Magni into the DX/D1 Front Speaker/headphone jack and get Headphone Surround Sound, thru the Magni.
The Xonar's GX software emulation of EAX 5.0 seems to be hit and miss (from what I've heard).
The Xonar DX, D1 and STX (& ST) all use the same C-Media CMI8788 audio processor.

 

[DJINFERNO806]

^This.
 
DX + Magni = Great combo that will run you cheaper than an STX/ZXR. 
 
But may god have mercy on your soul if you don't at least use the unified drivers...
 
serious....

 

[Solarium]

 
Looking at getting the Asus Xonar Essence STX?
You could get the Asus Xonar DX or D1 (used $60) and the Schiit Magni headphone amplifier (new $99).
The Magni has a headphone output impedance of less then 1-Ohm
So you can plug the Magni into the DX/D1 Front Speaker/headphone jack and get Headphone Surround Sound, thru the Magni.
The Xonar's GX software emulation of EAX 5.0 seems to be hit and miss (from what I've heard).
The Xonar DX, D1 and STX (& ST) all use the same C-Media CMI8788 audio processor.

The STX is actually only $170 on amazon, while as the DX is $80 and Magni is $100. The STX also have 1 plug for headphones and 1 plug for my speakers so I don't have to switch the plugs on the back every time, which would be a huge bonus. The main reason that I want to upgrade my sound card is to not having to use a headphone amp.
 
What about the ZXR, would that have lower impedance than the STX? Even with STX's 10-ohm impedance would it really still degrade the 50-ohm headphone SQ that much?

 

[stv014]

The ZxR has an output impedance of 40 Ω according to this test.

 

[SaLX]

  The ZxR has an output impedance of 40 Ω according to this test.

Whoa!

This is weird... they didn't do the same test with the STX for comparison, but for their Asus ROG Phoebus review they did (here), they got a result of 10 Ω which is more like it.
 

The output impedance of the average in the range of 40 Hz to 15 kHz Ohm: 40.9Ω (ZxR) (compared to 10.7Ω Phoebus sic).

 
I really don't know if this has any bearing on this: the ZxR results were based on a Frequency response from 40 Hz to 15 kHz dB compared to the Phoebus being based on a Frequency response range of 20 Hz to 20 kHz dB. Somebody with a larger brain please explain these values!!

  I'm sure that this result is skewed in some form or another.
 
Also here's stv's posts here on the subject.

 

[DJINFERNO806]

Ya that's the first I am hearing about the ZXR having higher than 10 ohm output impedance.
 
The headphone amplification stage is exactly the same as the STX, so I don't understand why it wouldn't have the same amount of impedance.

 

[stv014]

The headphone amplification stage is exactly the same as the STX, so I don't understand why it wouldn't have the same amount of impedance.

 
Both cards use a TPA6120A2 based headphone amplifier, however, the resistors that determine the output impedance are not part of the TPA chip. While 10 Ω is common (since it is the minimum recommended by the manufacturer), Creative might have chosen to increase the impedance for whatever reason. In any case, I cannot test it myself, since I do not have the ZxR, but on the Russian page the voltage drop with different loads consistently shows a ~40 Ω output impedance.

 

[DJINFERNO806]

Ya I did see on the headphone amp specs page TI recommends 10 ohms. But I don't get what purpose there would be to add more than a 10 ohm resistor.

Why would you want to decrease the damping factor? Or alienate customers with sub 320 ohm headphones.

Now I'm not very impressed if this is true as even my 250 ohm DT 770s may be subject to distortion. .....

 

[Fegefeuer]

Get an external DAC/AMP with <0,5 Ohm output and be done with it. It's the best setup to avoid any technical shortcomings and it makes your chain universal. 

 

[stv014]

Ya I did see on the headphone amp specs page TI recommends 10 ohms. But I don't get what purpose there would be to add more than a 10 ohm resistor.

 
TI recommends that as the minimum, but also notes that it can be increased up to 100 Ω if necessary. If Creative did use 40 Ω, then it might have been because of some shortcoming of their implementation. However, it seems manufacturers often simply do not care much about output impedance, and it does not have too much marketing value to the casual consumer either (it is usually not shown in the specs, and is not tested in most reviews that use a simple RMAA loopback). E-Mu (basically the same company as Creative) "pro audio" devices typically have an output impedance of a few tens of Ω, as does the previous flagship SB card, the Titanium HD.
 

Now I'm not very impressed if this is true as even my 250 ohm DT 770s may be subject to distortion. .....

 
I ran some tests on the DT880 Pro (250 Ω) recently, which, while not the same headphone, does use more or less the same drivers. I compared 10 Ω vs. 110 Ω output impedance, and the latter caused frequency response deviations of 0.5 dB, and a distortion increase of up to 2 dB. With 40 Ω, the effect would probably be reduced accordingly by a factor of slightly more than 2. So, it would not be major. By the way, if you have a splitter, you could also test the output impedance of the ZxR just to be sure.