Now that I have full Dirac bass management (and also Upmix) working w/o worrying about garbled sound, I spent some time doing an A/B (well, actually A/B/C). I found something I've never heard before... playing 2.0 material w/ full optimization or Upmix in Direct stereo I swear my center is on when sitting in the sweet spot. I can't convince myself it's not on, but, sure enough, it's not on (since I set the mode to stereo it shouldn't be). But, the imaging has improved w/ Upmix and full even over regular Dirac such that it's now impossible to tell. It's ever so slightly different than regular Dirac.