I’m not sure where you’re going to find a Phi TC for $4,000, much less with a suitable amplifier, anytime soon. The basic Phi TC alone has been going for $4,400 used.
The SR1a ups the game, across the board, on the HD800. Other than requiring some accommodation on the amplifier front, I can’t name anything I think the HD800 (modded or not) or HD800S do better.
Vs. the Abyss, if you don’t/can’t/won’t use EQ, then the Abyss will exhibit a higher bass level and better extension. And the difference is more in the sub-bass than the bass overall. Though it doesn’t match the SR1a for bass detail, texture, articulation or speed in my opinion.
If you do use EQ with the SR1a then you can get it to >=95% of the bass level and extension of the Abyss without any trouble. And still retain the SR1a’s superiority elsewhere.
Put another way … and this is just me of course …
After running the SR1a for a little bit, and playing with bass/sub-bass EQ some, I put my Phi CC up for sale - with the intention there being to “upgrade” to the TC version. A bit more time on the SR1a, finding I was slowly backing off the EQ (bass level comes up as the ribbons settle in, and I was using amplifiers that helped there too), and spending more time back to back with the Phi TC, I just decided to skip the TC version entirely.
And I’m still selling the Phi CC (very little demand; easily the worst resale value I’ve experienced on a headphone).
That’s not to knock the Abyss; it’s still my overall favorite planar headphone, despite its fussiness.
I’ll see what JPS comes up with after the Phi TC. It’s the best-placed planar to take on the extreme resolution, speed, detail and impact of the SR1a. But at this point, even if I pulled the trigger today, I am far from convinced that there wouldn’t be another upgrade around the corner by the time they actually arrived.