Alright, I sure let this project rest for too long.
Anyway, the mini controller was under heavy use for the better part of a month, I don't think those crappy pushbuttons were meant to withstand that much repeated stress, eventually they started becoming extremely unreliable, requiring intense force to register and also registering 2 or 3 presses at a time, leading to a lot of "Poor"s and failed songs :(
So.... here's my
intermediate controller, still not a full-on ASC with turntable. I'm using some microswitched pushbuttons left over from my arcade stick for the turntable part, but the key panel is basically arcade-accurate and I can remove it and flip it around for 2P side, but most importantly I can remove it and put it in the final ASC once I'm done the frame.
Lighted buttons OOOOOOOOOHHHHHHH!!!!! And it runs off the power supplied from the controller port, so no external supply is needed.
Testing: WOW, on the first day I used it, I instantly passed a whole bunch of songs that I was failing before, and improved my scores on pretty much every other song. Pressing the keys is so effortless now, my forearms never get sore. Too bad I'm still playing at a Light7 level...
And the cost so far? Less than what it would cost for a KOC plus shipping :p