Not hard at all to connect the power amp to the receiver. Use a speaker to line level converter to connect the front speaker outputs of the receiver to the amp inputs. Front left and right speakers connect to the amp. Turn on the amp and redo the set up on the receiver. Done.
Not much point in using the preamp unless you have a more audiophile orientation and want to play in stereo. Then you would connect the converter to the preamp and the preamp out to the amp. Any analog sources would be connected directly to the preamp so you could turn off the receiver. Set the preamp volume to the setting you would most commonly use, select the input you connected the converter and do the receiver set up. Mark this setting somehow so you can...