I remember having been one, it was quite a buzz being a crossfire mobo for AMD and all that, they had a few folowers. It got even better with the M2A32 (580x), but I can't seem to find it.
This problem seems to be also with the M2A-VM (which I happen to own) to reset the ram voltage at 1.8V. I haven't tested it since my M2A-VM rig is in a HTPC which is quite crowded already and doesn't need the extra heat from some ram sticks at 2.1V. I'm on the process of improving the air flow of my HTPC, so if I manage to try the ram at 2.1V and around 900MHz (they are ballistix ddr667) I'll let you know.
My take is that this seems somehow related to ASUS' implementation of ATI chipsets, as only the M2A (480x, 580x, 690G) and M3A seem to suffer from this.
M2N-MX ->Had issue with my Geil ram
M2N-E ->the famous 1.95 max voltage on ram
M2A-VM ->Had Problems with Ram, not compatible or something i dunno
M2A-MVP ->just simple shows me lack of performance, also, new bios takes away the ram settings for some oddball reason