On my Yamaha RX-A3070 AVR, I had been using Straight at the beginning of a film to see if I'm getting real Atmos or X - and if not, toggling over to Neural:X to animate my ceiling speakers.
Then I found the Auto setting for the AVR's Surround Decoder, which steps out of the way for Atmos or X, but applies Neural:X to DTS sources and the DSU to everything else.
Around the same time, I saw our host's comment that the DSU sounds better than Neural:X on stereo music, so I did a comparison.
He's right - as far as that goes - but neither of them sounds as clear as All Channel Stereo, which is a lot less processed, since it simply ties together all the channels on each side of the room (including the overheads) and sends mono to the center channel. (It of course does the usual bass management.)
I'll audition the DSU on stereo movie soundtracks, which are frequently designed with matrix decoding in mind, but not on stereo music.