On a Yamaha 7.1 receiver you can choose to use the back wall speaker pair for 7.1 or the up front presence speakers for 5.1. The presence speakers and the side surrounds are used in conjunction with DSP processing modes to generate a more spacious room, club, stadium, etc. atmosphere. Some people don’t care for DSP and if you don’t like the sound, you need not put up front presence channels. I have them put up and I use Klipsch bipoles for the presence channels and side surrounds. I didn’t have a room suited for 7.1 rear speakers so I tried the front presence channels. I like some DSP modes and I think the presence speakers are worthwhile. I think the DSP works better a non-live acoustical room as there may be to much combined echo in a live room.