Tear and compare. If one channel is working correctly start measuring how the DC voltages are different between the channels. If they are different ( and I would surmise if you're test 2200 uf 100V caps that your looking at the main filter caps ) which supplies are different, high voltage, low voltage? The input circuitry doesn't run at 80 volts or what ever the outputs devices run at. If the outputs are DC coupled as I remember some of the low end QSC were then a failed cap would not pass signal but all would likely be good up to that point. Do you have a scope, is it showing good signal on both channels up to the output caps? Large electrolytics do go bad with age and heat so not a bad thing to be suspicious of and relatively cheap to swap out.
