New Headphones

In the last 5-10 years a lot of new and EXPENSIVE HP's have been produced. I own a modified Hifiman HE-6 and the Sennheiser HD 650. The HE-6 is driven by my stereo power amp (Primare A32) with WyWires Red Series XLR cables and sounds fantastic. Alas curiosity is lurking. Are there any HE-6 owners/lovers (past and/or present) who've added or moved on to newer HP's for increased sound quality? Which HP's were added and what did they add that the HE-6 didn't give? (And in fairness) what amp did you use to power your HE-6 and what HP amp are you using to power your new HP's? I've owned (then sold) the Grado SR60 & GS1000E, Sennheiser HD 580 & HD 800, and the Audeze LCD-X. I've also owned and sold the Sennheiser HDVA 600 and Violectric V281 HP amps. Both were very good (but Violectric was the best of both) for my headphones. The first time I heard the HE-6 I was in love with it's sound (even unmodded) & was smitten by the bass. I'd never before had HP's where I FELT the bass vibrate my ears and head while having a detailed mid and upper range like the HE-6. Is there better? I've looked at the Hifiman Susvara HP because it also needs a powerful amp (I wouldn't need to buy a new HP amp) but that $6000 price tag is prohibitive. I've read the less-expensive HE 1000 V2 is pretty sweet, too, though not as sweet as the Susvara. I've also considered upgrading my HP cable to the WyWires Platinum which would be a lot cheaper than buying a new HP. I know Alex of WyWires makes a superb product and I wouldn't be disappointed.  I'd appreciate any and all input on this matter. Should I be content or go looking (listening)?

It's a moving target and it has moved significantly in the past two years.

Never a HE-6 owner, but I went from the HE-500 to the 560 to the 1K V1 and then to the Focal Utopias and I still own all four. 

Upgrading the cables is a wise choice and it will have an impact. In my opinon, a new set of headphones, different than the HE-6s, would also be a wise move.

I use a HeadAmp GS-X Mk2.

If you are not asking the same question over at Head-Fi, you should.....
Asked but no response from the Head-Fi folks yet. When you say a new set of HP's different from the HE-6's what would you recommend? I listen to many genre's of music and tight, accurate very-present bass is highly important (one reason I sold the Senn HD 800's). But I positively do not like equipment that produces a dark or warm sound (sold a Marantz PM-11S3 integrated amp and the Audeze X's because of this). I also need meaty mids and sparkly highs. Yes, I have the Senn HD 650 which some say is dark or veiled, but when these phones are balanced and well powered they are quite nice for their price. Sounds like your HeadAmp would pair well with them :)
I'd ask again, perhaps in a couple of different threads. Perhaps framed in a 'versus' way so the fans take up arms. : )

As you know, that's one of the best places to get headphone related info and feedback. Hopefully you will get the responses you are looking for.

You could reach out to Tyll over at InnerFidelity directly.

If you have your 6 optimized in the way I'm thinking, and you like their performance and signature getting something as fast and clean is going to be tough. When done right and paired well, they are exceptional, as you know intimately.

As you say Audeze is out; and I agree based on your requirements. Abyss??? 

The Stax SR-009 is likely the best fit for your requirements but will mean a new amp purchase as well which pushes the spend way up.

The other option, if budget needs to be listened to, is patience. Since you get and like the Fang Bian house sound, wait for the Susvara to drop in won't take long, given their recent history. : )
Got a couple of responses this morning telling me to stay with the "world class" 6 and if I really wanted to buy something the upgraded Platinum WyWires would probably be wisest. I've read Tyll's review of the 6's and he didn't seem to be impressed (too much treble) though I'm thinking he based his opinions on an unmodded pair. A head-fier also mentioned the Abyss. I've looked into the Stax but don't know if its bass would satisfy and for that price everything had better be perfect. There was talk on Head-Fi of the 4 screw 6's (leaner and brighter) having a different sound to the 6 screw (slightly warmer and closed). I have a 6 screw and I think it's fantastic. I'll take your advice on the Susvara, :) and wait for a price drop but in the mean time I am very happy!