I have an M2V, haven't tried coreboot yet, but flashrom works like a charm after some effortless tweaking. PLCC is socketed. The onboard flash chip still needs support in flashrom though. I flashed an W39V040B there, the M2V has a W39V040C. Then again, you should probably pick a bioas with a 8Mb chip. ASRocks are mostly crap, don't be surprised if they decide to die while in development.
Tiago