Do the two additional surround sound speakers need to be very powerful / high end? I have 2 SS-1's with my 5.1 speaker system. I accidentally bought 2 additional SS-1's (there were 2 in each box, although the Best Buy sales rep thought there were only one per box). Do I need to keep the SS-1's or can I return the 2 extra ones and replace them with smaller and cheaper surrounds? Also, I have two fairly cheap Radio Shack speakers - Realistic Minimus 7, input 8 OHMS, 40 W max. Will these work as presence speakers for my Yamaha HTR 5760? Thanks in advance.