Yes different amps will have different set ups. My system with PCM or analogue input will let you use pro-logic, or one of the upmix modes, but if you feed it AC-3 2.0, then that is what you get - and you can't override it! So to get surround sound from Dr Gonzo's disc for example, I have to use the analogue input!

The AC-3 audio on my DVD is correctly flagged as 2.0 Surround, so on my amp, the pro-logic mode is activated automatically.

I've always felt uncomfortable about creating a "fake" 5.1 mix from a matrixed 2-channel source; Dolby advise against it (but only because of potential problems with the downmix stage in DVD players for those using the analogue output). I suppose it comes down to a DanielB thing (go back and look at some old posts if you don't know who he is) of leaving the audio as original as possible.

I wonder if DanielB prefers the mono soundtrack to The Terminator like I do?