I've been pretty satisfied with the 990's upsample mode. Be aware, though, that you will not be able to use it in conjunction with any other processing - so no upsampling paired with Pro Logic II or 5 Stereo.
ahh..I did not know about that. I've always appreciated a GOOD surround system when listening to music on many recordings. Right now I'm listening to a live concert of Bob Dylan at Carnegie Hall recorded in 1964. I'm using the Pro Logic II decoding on my integra dhc 9.9 in my main system and I love the effect that surround mode gives to the music.
For a recording made that long ago, that Bob Dylan live concert is amazingly good on a high end system. The surround processor in my living room system now, where the 990 soon will be, is a 10 year old Harman Kardon Signature 2.0. That has Dolby Digital and DTS, but the pro logic is the older normal version..not PLII. It doesn't do nearly as good of a job on that Bob Dylan CD.
I'm looking forward to getting that 990 set up with the maggies and see what those speakers are truly capable of