Audio Systems: 5.1 Surround Sound Cutting Out, niles speakers, hdmi cables

Question
I have a Yamaha receiver, with inputs from cable TV, and a DVD player via HDMI.  The only output is to my TV via HDMI, and to the speakers.  The receiver is connected to in ceiling mounted Niles speakers (Front Left, Front Right, Center, Surround Back Left and Surround Back Right, and an Energy sub-woofer).  My problem is that when I have the receiver set on a 5.1 surround sound mode, the sound to the Front Left and Front Right speakers sometimes cuts out, with sound only coming out of the Center speaker.  It appears to cut out when there is a change of sound, and then it generally stays cut out.  If I have the receiver set on 2 or 7 channel stereo, the sound comes out of the speakers consistently and never cuts out.  When it cuts out if I flick back to stereo and then back to 5.1 again, it sometimes corrects itself, until the next time it cuts out.  Some sound sources seem to be more problematic than others.  Sometimes it behaves for a quite a while, and sometimes it cuts out quickly, and sometimes it appears to cut out when there is a change of sound.  I know its either something to do with the Receiver or the speakers because I have disconnected all HDMI cables….. this means the only input is from my cable TV unit, and the only output is to the speakers, and the problem still occurs.  I don’t think there is an issue with the receiver because I have trailed a replacement receiver from my store and the problem still occurs.  Therefore I assume there must be a problem either with the speaker cabling, the speakers, or the way the receiver interacts with the speakers.  The baffling element is that there is absolutely never any problem in stereo mode (over months of operation), only when using a 5.1 surround sound mode.

Answer
There is some processing involved with 5.1. There is a 5.1 test DVD that produces pure tones. If you carefully checked all of the output and speaker connections and the problem still persists, using that DVD you can check voltages with a meter to see if there are any discrepancies between channels at different volume levels. You may also try testing the receiver with new cables loosely run to the problematic speaker channels and see if it still occurs.

Having been in the industry for 40 plus years I've seen some very odd nearly unexplainable scenarios. I did however always persevere until I solved the problem including if it meant replacing every element of the equation.

Good luck. Let me know if I can be of any further assistance.