I found a local dealer who is cutting me a good deal on a QSC USA sieres 1310 power amp. I realize this is an older and discontinued sieres, and its massive (4 rack units), but I believe it'll work for the purposes I'd be using it for. One thing I notice is that the gain knobs are on the back. I've never had a power amp before, so I'm wondering if this will be a problem. Also, Ohms and impedance blow my mind, so this may sound stupid, but how does a poweramp/cabinet knows what ohmage to operate at (Say the power amp is rated at 400 watts @ 8 ohms, and thats the max handling of the cabinet its attached to). What kind of experiences have any of you had with the QSC american sieres. Thanks for your help.