I ended up taking my DT880s to a local electronics repair shop since I didn't want to have Brian work on broken headphones and the factory center isn't open yet. The guy had good reviews and seemed competent (I left the first shop as he used a multimeter on two pieces of metal the didn't even complete a circuit).
Anyway, he said he'd put a new end on and have them back to me in a day. Three days later I call him up and ask what the status is and says he's perplexed and has seen nothing like it before. He's taken it appart and put it back together and it still has the same problem. He said both drivers appear to work perfectly individually and depending on what he plugs it into, sometimes they work at the same volume, sometimes different volumes. The TRS checked out and the cord checked out.
He doesn't want to change any components because he said everything works, but when the headphones are put back together, the left channel is just much lower than the right on some devices. He said he was using them on a Samsung CD player as I called and they worked, but he's tried them on other sources and they don't. He said if he can't figure it out tonight, he's going to call Beyer and ask if they've ever run into this problem before.
I paid him $20 to diagnose the problem and his assistant said he was working on them yesterday when I called, and he was working on them today when I called...so I guess I'm getting my money's worth, just wish I had headphones. My inclination is still a bad TRS, but he said the TRS appeared to check out and he didn't want to change it until he was sure.