AJA Io setup w/ Roland speakers, must turn speakers all the way down

So I've got a dual 2gig G5 with an AJA Io and I'm monitoring sound through a set of Roland MA-12 speakers. We use four channel sound, and the way I have the speakers hooked up is my left speaker gives me channel 1&3, and right speaker gives me 2&4. The only thing is, when I'm inside FCP, I must turn my speakers all the way down, in order to NOT blow out the speakers. The G5's mini-audio out is also connected to the speakers, and when they're turned down while I use FCP, I can't hear any of my system sounds. Is there a better way to set things up? Or did I just screw a connection somewhere along the lines?

Thanks for your help.