I tried the Neural THX 5.1 and PLIIx Music mode with a few music CDs.
I'm not sure if it's cuz I'm running dipoles as surrounds, of if it's the position of some of my rear corner treatments or what but Neural THX does not sound as crisp and detail as stereo sound. The voice is anchored more at the center channel but everything else (my preference) seems not as clear and or airy.
The PLIIx Music mode sounds better on my setup. It's more clear and it's more immersive than Neural THX 5.1.
Even with the PLIIx Music mode being more immersive, I still think I prefer 2 channel Stereo mode the most (with the SubMersive). It's the most cleanest, clearest, crisp sound in my room.
I'm starting to wonder how much my opinion would change if I had some direct radiating Triads for surrounds vs. Sapphire Dipoles
I guess I'll have to wait a while before I find out - no rush though as I am still thoroughly enjoying this setup.