Gonk,
Thanks for all of your info here. Very interesting and informative. Regarding upsampling and DD...

If one has a 7.1 speaker set up, but chooses the DD 5.1 for the SS instead of PLIIx, does upsampling still work or is the 7.1 speaker set up an issue?

If you select "Upsample" for the processing mode (using the "Stereo" button on the remote - like sportsound said, it's a trick and is not documented ) than the 990 will still decode the DD 5.1 track (as it has to in order to get any audio) and will upsample it while it's at it. However, you just defined your processing mode by doing this (techically it would be "Dolby Digital + Upsample", but it's simply called "Upsample") and there's no way to add another processing mode to the mix, so you can't further enable PLIIx. I haven't tried a flagged Dolby EX track, but I suspect that the EX flag would force the unit out of "Upsample" and into Dolby Digital EX.

me too. only left and right stereo when using upsampling.

Is the source only a stereo source? If it's a PCM stereo or a Dolby Digital stereo source, upsample will get you only stereo. If it's a Dolby 5.1 source, however, you should get the full 5.1.

I read these posts in haste but hope somebody pointed out that upsampling can apply only to digital inputs, not analog. I.e., it's meaningless for tuner, tape, and phono. I know some of you still use the last two.

Actually, upsampling can be applied to analog inputs, assuming we're not talking about analog inputs set to bypass (which of course skips the digital section) - non-bypassed analog signals are converted to digital, at which point upsample is an option.

That is what I have experienced.Material that is 2 channel will only come from left and right in the Upsample mode. If it's a TV show or broadcast movie that comes in that way I press the "Stereo" button, revert to "Stereo" and THEN press "Dolby Modes" on the remote to choose PLIIx. Not very elegant, but I don't mind pushing a few buttons.