Don't have a Mac but according to the lit, there is a switch on the back for mono operation. Typically, but not specifically to the 2205, you would flip that switch to mono, use only the right channel input only (both amps) and connect the speaker wires to both left and right positive (+) terminals on the amp. Again, I can't confirm any of that specifically for the 2205. My experience is with Plinius and has been positive.
Macs are ruggedly built and the output impedance is halved when bridged this way (0.5 ohms). If the Infinity speakers are the same vintage, this should be a benefit.
There are many amps that should not be bridged but I doubt you could damage the Macs unless you screw up the wiring. I remember reading in the Plinius manual that connecting the negative(-) speaker terminals could be fatal to the amp but it's a possibilty the Mac mono switch is more inclusive. I also don't have independant gain knobs to deal with but I doubt that should be a problem.