YM2608 Document from Yamaha
Someone got ahold of the official Yamaha documentation of the YM2608, from which the YM2612 directly descended from. Was in Japanese, but someone gave it a wonderful translation to english. It tells pretty much everything you needed to know about the YM2612, even the fine details that no other document even mentioned (like the flashback/GEMS sound bug).
I'm pretty sure quite a few Genesis emulators will be getting some major audio updates soon.