Speaking of music...
Well, the problem with 2-CH Stereo and upmixing with DSU are the completely different results, dependend from genre, original mix and other things. For example Electronic and similar music mostly gains from DSU with simply more atmosphere - the immersive bubble effect makes sense here, if someone like it that way... me including.
But, a well defined recording of jazz or rock with a distinguished stage is going to confuse you in DSU mode, e.g. with a sudden appearance of the lead singer or the bass guitar right besides you at the couch or even more irritating from upwards behind.
That's not, what I want here and I agree with Roger in order to demand more control about the upmixing.
On the other hand, Multi-CH concert recordings mostly profit from DSU, especially those with live atmosphere. In the meantime I tried a lot of music / concert Blu-rays and in 90%, DSU is great.
So, my default setting is "Stereo" for 2 CH Stereo and "Dolby Surround" for all other inputs. If I'm just in the mood to listen to e.g. Jean Michel Jarre in 2-CH, then I try to switch and after a very short moment, I know, what I have to do...
Home theater room with a 7.2.4 setup,
Yamaha CX-A5100/MX-A5000, Epson TW4400, Oppo 103D,
nubert nuVero series 14/7/3/5 speakers