You can. Jeff is correct-it is page 22 in your manual. Use RCA Interconnects from the preamp outs in the lower left of the rear of the receiver to the applicable RCA inputs of the separate amplifier. You won't lose any of the surround modes. I would think, though, that if the Marantz outputs 90 watts while running all channels (some surround sound receivers power the max output into two or three speakers and than it is reduced as it powers more) and if you really need power, going with 125 watts may not be worth the cost of the amp and cables. I have a Pioneer Elite receiver @ 130 watts per channel and have an extra three channel 150 watt amp and not hooking it up as I just don't feel the extra 20 watts is worth the work and interconnectss. (I am eyeing a Mcintosh, though). Maybe you should look at a 200 watt 3 channel amp.