Have chatted with Peter at Double Helix cables today. Will post some of his remarks below.
Beyer surgery nearly done
adapters built, just attached first one
When you take them apart, you can see the cups are way more shallow than they look, they actually don't have at all the same design as the T1. So these will have Triple Threat adapters 8 wire silver litz, even those barely fit the stock strain relief.
The holes are too wide for hifiman or hd800 terminations, but the cups are too shallow for audeze.
Right channel reassembled, looks/sounds good, onto the left, adapter built, attaching now.
Again aside from maybe 2 extra inches of wire, there's no difference between this mod vs. a jack.
Mod complete.
Yes you have the nastiest T5P's on the face of the earth.
Only ones with silver litz.
Only ones with 8 wire silver litz.
God these sound infinitely better.
I didn't honestly like them much when I first got them.
So much air.
Internally the cables are secured with plastic zip ties, although the fit is so perfectly snug with the rubber stock strain reliefs that it practically didn't need that, but no nasty glue flood in there or anything.
The stock cable isn't much.
Yep these look/sound terrific.
These were pretty unrefined before, to be perfectly honest. like, very good for portable cans, but not world-class.
Right now they're a can that I probably need to purchase.
Very very clean, but not harsh like hd800, they are laid back while being perfectly clear.
Very comparable to HD800, but they're essentially a closed can.
I think they're a little less fatiguing, still decently bright cans, beyer goes for super neutral studio type sound.
Ideal for jazz, classical, classic rock.
I think they'll have even more bass if we got them some different pads, some cushier aftermarket full leather ones would be nice.
I don't feel like the pads seal as well as they could, this is a problem with most Beyers.
These have the most elaborate drivers just about that I've ever seen.
The magnet structures are a work of art.
Going to put some clear PVC shrink on the plugs to keep em smudge free but other than that it's all done.
Peter, I hope you don't mind if I post some of your comments from here in the T5P thread?
Sure, have at it.
Yeah you can let em know that hanging adapters are the way to go, and functionally they're a better signal path than what is stock on hd800, audeze, or hifiman.
And similar to the earcup jack mod just with a few inches more wire length.
. 
the fostex th900 seems to be my last chance of closed back high end!(also posted on xc thread)
