Got mine today!! These have some magic going on!! I really liked them right away, then about an hour or so in, they really opened up. I couldn't quite put my finger on what it was, but it was special. After listening another hour or so, I finally figured it out. They make it sound "Live"...

The paper towel mod really fixes that. Just that little bit of extra dappening reduces the reflections that are causing the echo-y, edge-y sound and really makes them much clearer. I haven't received the Vegan pads to try yet, but the paper towel mod is a must IMO. @cskippy really nailed it...

I would say save up a few more dollars and get the Fostex T-50rp MKIII.  You can find them usually on sale around $120 US.  Pretty good budget planar.  

Yes. Not actually boosting, actually cutting everything else.

I did look at those, but ultimately was pretty happy with the 400I. I also don't always boost the bass that much, just helps electronic music. Haven't been using these as much now that I have Lcd 2 and Nighthawk. I do up the bass similarly on the Lcd 2's as well for electronic. And they sound...

I bump the 30hz and 60hz up 6db, and 2k region up 3db.  Everything else is flat.  

The Valhalla wouldn't be a good amp for these.  You want a hybrid tube amp, or SS.  Some options for the Valhalla would be the Senns (600, 650, 700, 800).  

That is super easy to fix.  Just pry off the ring that is holding them on, take them out and straighten them.  Then pop it back on.  Or if that isn't sufficient then replace them like they used to do with the small waste paper basket mesh.  

Schiit Jotunheim is well regarded.  Also, Modi Multibit with the Gustad H10 is very good.  

I would go for the Valhalla or the Lyr. The Valhalla was a better match for the 700 then the H10 IMO. Haven't heard the Lyr, but it would be the most versatile.

As for the bass, these EQ very well. So, increasing the sub bass is pretty easy.

They are both good. 400I is more neutral. Nighthawk warmer

I agree. I would say the Nighthawk is a better 650. They have similar sound signatures, but the Nighthawk has better bass and treble extension plus better clarity and speed. It's a very resolving HP. SS is a little wider on the 650, but depth is better on the Nighthawk. Nighthawk is a little...

Has anyone mentioned the Fostex T20 MKIII?  I think those are really nice, bassy HP's for under $150.  They need some power to sound great, but damn, they sound good.  

Fostex T20 mkIII are good. That plus a Schitt Magni or an O2 would be a good budget combo

The Uber should have plenty of power for them.  Might be something wrong with your headphones. 

That's some seriously good info.  +1

That's fine, I still think the 700 is a technically better HP.  Saying that, there is something special about the 650 as well.  It has a combination of lush mids with just enough treble detail to make most songs sound really good.  Especially acoustic.  It's a great all around HP for long...

I thought it sounded better on Hi gain as well. It sounded fuller on Hi to me.

I was only talking about the Bass there but I also agree with you on the Highs.  Overall, I find the 700 more enjoyable except for long listening sessions (>2 hours) where the Highs may slightly fatigue.  Of course, having a decent tube amp helps and may eliminate that for some, but I found that...

I would go with the 400S. It´s the better choice for your amp.

Do you have an amp, and if so which one? Are you planning to get one?

650 has more mid bass, 700 has more sub bass and is more detailed, faster, more accurate.

Yes, it is a very good combo especially with planars.

I would say they sound similar as well.  I had both at the same time for about 2 weeks.  560 is more detailed, larger SS, and a little colder tone.  400I is more intimate, and slightly less detailed, warmer with a little more bass.  This is listening to classic - modern rock/ electronic on Tidal...