Holy crap, I didn't even know about the TR-90 before now. That's a bit confusing.
First thing that came to mind was the Fostex TH500RP, which looks like the basic TH body, save that it's open-backed with planar drivers. I guess the ___RP designation is for planars (e.g. the above or T50RP), while TH-___ is for... no idea. The TH line has had detachable cables before in the 900 mk2 and 610. TR for "removable"?
Massdrop TR-X00 and TH-X00 only differ in the removable cables. And the connection is inverted polarity from the HD6XX cable, with deeper insertion (shallower shoulders). Use the Furutech FT-2PS-F (note the F) connector if you can find them. Otherwise the normal FT-2PS(R) can be filed down to fit properly.
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