I believe the good doctor is running Kodi, as I am. Its a setting in Kodi, not the NUC hardware. I can't remember the exact terms, but one option is to specify a fixed output regardless of the actual file format. So, for example, if you specify a fixed output as 24/96, 5.1 channel, everything that is played will be output as 24/96, 5.1, even if it is only 16/44.1 stereo to begin with. Kodi will add the empty channels and increase the bitrate by adding zeros. If the track is actually of higher resolution like 24/192, 5.1, Kodi will transcode the track to 24/96 by removing bits. This allows the AVR to always only see the same incoming format, so it never tries to switch formats.
An alternate option within Kodi allows it to choose the closest output format relative to the file type. If set this way, Kodi will stream 2.0 16/44.1 when that is what the file is. It will also stream 24/96, 5.1 when that is the file format. If it encounters something strange like 20/44.1 it defaults to the closest available format (maybe 16/44.1 ?). However, this type of format switching makes many AVRs drop the first second or two of the track while the AVR adjusts.
JRiver may have the same type of option. Its been years since I played with JRiver, so I cant say for sure.
Yes, I understand and my set up on JRiver is very similar. I do not there is a button called pseudo surround on JRiver for 2.0 but I am not sure if that also changes the bitrate. I am sure all the playback software company's have very similar setups.
I will say I love my stereo and my surround and I don't think I would like everything to be surround.