Keep r_multigpu at 1.
Crossfire has matured since last I used it, and there shouldn't be any BIOS settings to change I guess. That said, it couldn't hurt to look.
Couple really simple things to check (pardon me, I don't know how proficient you are)
Make sure you're installed to the correct PCI-e slots. On your board, these are quite obvious (the only ones with locks)
Are you using a bridge, and have you tried both bridge connectors, and have you checked the bridge itself for damage?