This may be a dumb question, but since all five inputs to the amp are connected to the preamp, do I need to do anything (setting, etc) so the amp knows only two channels of audio are being sent?See page 46 in the preamp manual. Just press the "stereo button" on the remote is all you need to do. Then only the front L & R will play, and no signal will be sent to center and rears.
Does it matter which channels I use for fronts, center and rears.Probably not, however, looking at the back of the A51, color coding indicates that,
Ch1 - R front
Ch2 - L front
Ch3 - center
Ch4 and Ch5 - rear, but no indication for R and L, so just make sure you are consistent with connections.
You're welcome, and glad to help.