Just to update, I tried the Raidmax with just the 20-pin connected to the mobo and it works fine without the 4-pin.
Odd.
I've been on the other end of that problem before, where the mobo will not power up without the 4-pin and 20-pin both connected. I'm pretty sure in my manual it says to use both power connectors... oh well, it seems to be working nice and stable with all components drawing from it--so far.