I have dolby digital on my Onkyo (in addition to some other stuff). Onkyo builds on the Dolby digital to add additional flavors of the Dolby Digital. I read the Onkyo documentation to get a hint of what they are doing. It seems to me that Onkyo does an awful lot right once you get through the marketing speak and get the gist of what they are doing technically. For example, the room correction software focuses primarily or only on breaking up standing waves in the bass and doesn’t seem to touch anything above 200 hz. Perfect. Right in step with Dr. Toole’s book.
Anyway, I tend to choose upmixing options, Onkyo flavors of Dolby digital, that exaggerate the least effects (like reverb or delay or whatever they are extracting out of the original recording) but still upmix the stuff around. I guess you could say I’m looking to maintain a dry, precise sound, but with the obvious immersive benefits of upmixing. The Onkyo Dolby Digital based “Unplugged” variant seems to do this well for me, for example. The upmixing options and apparently the room correction algorithms have improved with firmware upgrades, and they do seem to work in tandem, which I’m very pleased about.