Something sounds very strange/wrong when playing back stereo audio (only) vs video in pseudo-surround mode. Tested stereo or 2.1 vs 7.1 channels.
You can try this yourself by using one of several Youtube audio and video downloaders... either way it produces the same results. You could also extract the stereo audio from a stereo video file already on-hand.
The mp3/m4a audio-only file plays as expected when upmixed, but the video (with stereo audio) track sounds completely different -- much worse, I'd say broken even.
Common left and right sound is mixed and moved to the center channel plus completely removed from the left and right channels.
Unusually strange bias in DSP processing since both audio and video tracks provide the exact same stereo channel content to JRiver. But it's not just that... everything else in the pseudo-surround upmixed video sounds wrong as well. Again, while the audio only mp3 or m4a file sounds perfectly fine.
I've noticed the exact same behaviour between my Linux and Windows PC (JRiver version 33 and 32). Regretfully, I uninstalled version 29 and its backup a few days ago so could not test it as well.
Didn't notice this for quite a while since I always send stereo optical/toslink audio from my Linux PC to the USB input of my Windows computer for upmixing (there's no WDM feature in Linux). This means stereo audio and video both get treated the same way -- i.e. there is no DSP upmixing bias: pseudo-surround mode sounds exactly the same between audio and video stereo media.