My brother has a Denon AVR-688 Receiver. It is set to 5.1 Stereo and we can't figure out how to switch it over to 7.1 Surround. I built him a room in my garage and prewired in the walls for four hanging speakers. We also have a Center Speaker mounted above his TV. There are two tower speakers on the floor. A total of seven speakers. I wired the first two speakers on the wall as Front A left and right. Center speaker as center speaker. Second two speakers on the wall as Surround A and B. I wired his tower speakers as Surround Back\/Amp Assign A and B. His receiver on 5.1 stereo will not play the Front A left and Right. I believe we need to switch the receiver to 7.1 Surround to get all the speakers to work. We have to do it manually because he no longer has the microphone for audio auto setup. We can't get it to switch over manually. I see in the manually that under the heading "DSP Simulation Playback" there is an option to switch from 5CH to 7CH. It won't switch over here. I see a foot note that says 5CH will be displayed when Surround Parameter "SB CH OUT" is set to off. Which I am assuming forces 5CH stereo only. I checked the SB CH OUT and tried changing to different options and we still could not get to change over to 7.1 channels. Does anyone have the knowledge of what we should do at this point to get it changed over to 7.1 channels? Thanks in advance.