I've had my 6-speaker/Dolby 5.1 home theater audio system for about four years. Unfortunately, the center channel has suddenly started working intermittently. I thought I had the problem solved at one point, only to turn on the system again with the same problem--no signal to center speaker. I've thus far determined: 1) The center speaker works fine (when connected to any channel other than the center) 2) Swapping speaker wire makes no difference 3) All other speakers work fine I think the problem is the amp, which makes me real sorry. The amp is a 4-year-old Onkyo TX-SV454 Audio Video Control Receiver. Anything I may have overlooked? Thanks!