Sennheiser HD600 and Focal Spirit Professional.  LCD2 are a bit too mellow and HD800 are too bright.

Haven't heard the FSP but I agree with the rest.

I think the "Natural Sound" still emblazoned on the HD 600 outer box is on-point.

Maybe it's the paint after all.

I've been trying to find the most tonally balanced headphone myself. Among those mentioned, right now I have an HD600, DT250-250, HE6, Paradox, HP50, and something which I feel ought to be mentioned, the Sony MA900. They all sound good, but have some caveats:

HD600: It's a little closed in sounding, lacks sub bass for some genres, and is generally unexciting. Pads need to be changed very often or the imaging can get muddy.
DT250-250: Exactly the same as the HD600 but worse ^ It's also rolled off on both ends compared to something like the HE500. But then it's also closed and is extremely tough. Listening to it with a Vali alleviates the problems somewhat.

HP50: There's a little bass emphasis, and the nasally characteristic gets in the way of clarity. However, it might be a selling point of these cans. They mentioned "room feel" in the marketing material, and it seems the honky sound is there to give an impression of more space(?) I think it's great, but I generally use it as a portable and never for serious listening.

HE6: Etched treble. I don't think it's neutral. Sometimes the treble can get painfully sharp on contemporary pop stuff. I hardly use it because of my issues with the highs, but I think it's great for vocals. The presentation could also be wider.

Paradox: What Dave said earlier. Re: the bass however, the Paradox does have bass if I press the cups in tighter. I'm currently experimenting with replacing the headband and pads for a tighter seal. The Paradox I think is the most neutral out of the headphones mentioned, except for a small issue with the highs that some people really don't like. It makes the HD600 and DT250-250 seem warm in comparison.

MA900: Most comfortable headphone I've owned, and reasonably neutral (in the HD600 sense). It lacks lower bass impact even though the bass is there, probably because of the air gap between the drivers and the ear. I'm a little scared to bring it out of the house though. The highs are reasonably detailed but are a little soft. You can take a look at the FR on GE

Again, I like how all these headphones sound in general which is why I own them. I just wrote about the problems I have with them despite a lot of people calling them neutral.

The ones at the top of my list to try - Spirit Classic, Slant, Enigma. The big Orthos I just find to be too heavy. My favorite headphone in terms of comfort remains the SR-007MK1 I used to have, but it was ultimately too polite for my tastes and I moved on.

I think I would have to skip Focal spirits due to the clamp... I am very allergic to that. I will skip Viso HP50 as well. I am thinking about Paradox or Slant as Enigmas are most probably a bit too coloured for what I am looking for - and as well more expensive.

I've been trying to find the most tonally balanced headphone myself. Among those mentioned, right now I have an HD600, DT250-250, HE6, Paradox, HP50, and something which I feel ought to be mentioned, the Sony MA900. They all sound good, but have some caveats:

HD600: It's a little closed in sounding, lacks sub bass for some genres, and is generally unexciting. Pads need to be changed very often or the imaging can get muddy.
DT250-250: Exactly the same as the HD600 but worse ^ It's also rolled off on both ends compared to something like the HE500. But then it's also closed and is extremely tough. Listening to it with a Vali alleviates the problems somewhat.

HP50: There's a little bass emphasis, and the nasally characteristic gets in the way of clarity. However, it might be a selling point of these cans. They mentioned "room feel" in the marketing material, and it seems the honky sound is there to give an impression of more space(?) I think it's great, but I generally use it as a portable and never for serious listening.

HE6: Etched treble. I don't think it's neutral. Sometimes the treble can get painfully sharp on contemporary pop stuff. I hardly use it because of my issues with the highs, but I think it's great for vocals. The presentation could also be wider.

Paradox: What Dave said earlier. Re: the bass however, the Paradox does have bass if I press the cups in tighter. I'm currently experimenting with replacing the headband and pads for a tighter seal. The Paradox I think is the most neutral out of the headphones mentioned, except for a small issue with the highs that some people really don't like. It makes the HD600 and DT250-250 seem warm in comparison.

MA900: Most comfortable headphone I've owned, and reasonably neutral (in the HD600 sense). It lacks lower bass impact even though the bass is there, probably because of the air gap between the drivers and the ear. I'm a little scared to bring it out of the house though. The highs are reasonably detailed but are a little soft. You can take a look at the FR on GE

Again, I like how all these headphones sound in general which is why I own them. I just wrote about the problems I have with them despite a lot of people calling them neutral.

Wow, thanks for your comparison, really nice! I was thinking about MA900 at some point but skipped in the end...

Have you heard Nad Viso HP50? If yes, do you find them similar enough to Spirit Pro? Viso HP50 are easier to purchase here...

The Focals sound more linear to me, whereas the NAD sound like they were voiced to try and wow you... added treble emphasis, a some added bass, etc. I actually think the NAD is a pretty good all-rounder, though it doesn't sound that natural to me. It gives music this artificial veneer. Reminds me of the scene from the film Jubilee where a man is tending his garden of plastic flowers and discovers a poor caterpillar trying to eat a fake leaf.

The Spirit Pro can sound a little timid or weak-kneed by comparison. However I think it's the better headphone overall for my tastes.

Of the recommendations folks are giving, I'd say the Paradox Slant is probably the best overall in your price range. If I could only choose one for myself, it would be the Slant for sure. Don't get me wrong: the Focals are great, and I think Focal put more effort into their products than many other speaker manufacturers out there who seem t regard headphone listening as a profitable afterthought.

The Koss ESP 950 is an exceptional value, and it's something that'll grow with you too should you decide to upgrade the amp down the road. When paired with a good Stax amp, it becomes a whole 'nother animal. One to be reckoned with, I reckon. Only think is, the build quality really is pitiful. The drivers are most likely going to develop the dreaded crackling issue at some point, and you'll really need to take advantage of Koss' lifetime warranty. Multiple times in many cases. If Koss packaged it in a fancy frame and tightened up their tolerances for production, they'd have something every bit as capable as Stax's offerings.

How would you compare the bass on the Float to other high end headphones?  Does it sound similar to any HPs I'd know or is it completely different from the other electrostats?

I don't have my Floats set up right now, so Shipsupt could probably do a better A/B comparison.

In a way the QA's bass response brings to mind the Jade's which, in turn, reminds me a bit of the better LCD-3s. More in quality and not quantity: the QA isn't a bass heavy pair of headphones, but it can throw some heft around when it's called for, all the while still maintaining a linear low-to-midrange transition. I suspect those massive earspeaker panels so close to the ears results in better low-end performance. Doesn't have quite the same level of control as the Abyss however.