Update, if MPC is running in a different directory, I can run 2 instances. You just have to rename MPC.ini to mplayerc.ini, in the settings set the output to the other soundcard, close, then rename to mpc.ini again.
In RRconfig I set the start command to VIDEO, and on the second instance, it went immediatley to the video screen. I can just delete all the other parts of the skin I dont need.
Now I just need to find out how to control the second instance of RR's MPC from the 1st instance/screen.