Not sure if I mentioned this in the thread, but I have had some negative experiences thus far with the actual Dolby Surround system on 2.0 stereo sources -- starting with a marathon of Friday the 13th films I did on DVD last month, some of which contained Dolby Stereo 2.0 tracks, I noticed that when processed via the Denon's Dolby Surround algorithm, these signals exhibited nearly no surround information where there should have been. And I say "should have been" because in the past, watching these discs on older AVRs via the Pro Logic II Movie mode, a good deal of ambient information was extracted from the stereo signals and put into the surrounds. When I watched these same discs with Dolby Surround engaged, the tracks came from the center with some left/right spread...nothing much of anything going on in the rears.
Over the past couple of nights I watched the 1978 Dawn of the Dead "DiviMax" DVD (from Anchor Bay; came out around 2004 in conjunction with Zack Snyder's remake at the time), and at first I watched the film with the DTS 5.1 mix (which I usually do; the mix is weak and front-heavy). When I finished the film the second night, I tried the 2.0 surround audio option (this release has a multitude of redundant mixes, including an original mono track) and, again, the Denon's Dolby Surround upmixer threw nothing into the surrounds -- the entire track was center-focused with some minor left/right bleed. Now, it is, of course, entirely possible that Dawn of the Dead's 2.0 mix (this was the first time I watched this disc without running the 5.1 DTS surround track) didn't really have any information to extract into the surrounds, but given my experience with the aforementioned Friday the 13th films and the way Dolby Surround handled those, I suspect there's something else going on here.
Either I got a defective Denon, or Dolby Surround is a bullshit matrixing system compared directly to Pro Logic II (which some other folks have agreed with).
