I think he's talking about the disc player that defaults to PL II, I think that because my DVD-C750 does the same thing.
I do not know how to defeat that "feature", but I do know how to get it to stereo without going into the menu; there is a button below the power button on the remote labeled "sound mode", press that until "stereo" appears on the players display.
No.5 is correct. When I said "it" switches I mean the DVD player switches to PLII. Sorry for the mixup (and yes it is a stereo amp so no setup required there).
I've found the "Sound Mode" button on the remote and yes it is very easy to switch to "Stereo" that way but the CD Up Sampling has been switched off as a result of going into PLII and the only way to switch that back on is through the setup menu.
In other words for each and EVERY CD I firstly press "play" (which switches to PLII), then "Setup", then navigate to "Audio" and switch on Upsampling (which also switches on "Stereo") - very boring.
Looks like I may have bought a medium quality DVD player (as a backup) rather than a CD player with Upsampling. I bought it refurbished on the web so (a) cheap (50%) and (b) difficult to return.
I did my research before hand but a quirk like this is not obvious - bummer