I tried moving the slider, but still had the problem. I knew it was still a problem because as I was browsing the internet, the problem would be triggered by scrolling down a page. Then I decided to try changing Soundmax Digital Audio to Primary Sound Driver in Output Device. This seems so have cleared up the problem. Strangely enough tho, I changed back to Soundmax Digital Audio and the problem has not recurred, however, I now have only one channel either way, but only when I switch output to the speakers, headphones are fine. I also have both channels when I switch to CD player on the amp, so the speaker connections are ok. I tried a Youtube video and the same prob.
The Computer is connected to the stereo amplifier via a brand new Monster cable.
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I am ready to order a new sound card...