I have a 7.1 set up, using a Yamaha RX-v1000 receiver. I am using the 6.1 (rear center) preout from the Yamaha and running it to an old Sony receiver (acting as an amp). I then have the rear center speakers connected from the Sony's MAIN (L-R) speaker output. This works great but for some reason there is an awful "hissing" or "buzzing" sound coming from the speakers. I have all of the speakers at the same dB level (used an SPL meter) but the rear centers are the only ones hissing. I assume it is something with the Sony receiver that I am using to power the EX channel. Any ideas how I can get rid of this problem? It is driving me nuts.