1. Surround backs are set "small".
2. The surround mode is set to "auto". The manual defines "auto" as:
"In this mode, the type of digital signal input, such as Dolby Digital, Dolby TrueHD, Dolby Digital Plus, Dolby Digital EX, Dolby Atmos, DTS, DTS-HD, DTS:X, DTS-ES, PCM (multi-channel) is detected, and the playback mode switches automatically to the corresponding mode. If the input signal is analog or PCM (2-channel), stereo playback is used. For Dolby Digital or DTS, the music is played back according to the respective channel number."
"Auto" seems like the smart choice since my library is a mix of stereo, 5.1, and 7.1. I don't want to have to change modes (or try to remember which files require which mode) every time I play my media.
I should also add that it doesn't matter what surround mode I pick. This is happening in all modes (except 'virtual' where it fakes 7.1).