I think the M3 would fit the bill nicely. Has a bit of a bass hump which gives it a fuller sound--from what I've gathered from the forum here.
What kind of power does that M31 put out? I have a Denon UM 50, or something like that, I used in college. Used it mainly for headphone listening, but I remember reading a warning about damaging speakers because it did not have enough power. It came with some Mission speakers that were specifically designed for the Denon Micro unit.
By the way, welcome to the boards!
"Nothin' up my sleeve. . ." --Bullwinkle J. Moose