Try changing ROMSTRAP if the M2V-MX SE works than it might be this. Go to the src/southbridge/via/romstrap.inc and change the romstrap to use the K8T890 instead of K8M890. I think both differs only in one byte 0xaa versus 0xff
In other words check if with changed ROMSIP something changes. I guess this is the only remaining difference between the SerialICE and coreboot.
Let me know if this works for you.