Is your receiver a Dolby Pro Logic or PLII? I had the same problem with my 1991 Vintage Technics SA-G710. The surround channels were actually 60W instead of the 130W/C for the mains. I noticed that the sound quality in the surround channels was not the same as the mains and there was hiss when no input source was selected. In contrast, I could turn the volume all the way up and hear nothing but silence from the mains.

Sean

Exaudio ergo cogito ergo sum