The 5-channel and 7-channel stereo modes are exactly what they claim to be: left channel data is copied to the left surround (and left rear surround in 7-channel), right channel data is copied to the right surround (and right rear surround in 7-channel), and the left and right are summed for the center channel. You tend to get a higher overall SPL level at the same volume setting because of the additional sources. I've used it for background music and been pretty pleased with the result.