I have 990 and feel audio qulity far surpasses 950.
Does upsampling only occur when fed a digital input? Or will it also act on analog inputs?

I was thinking that it worked for both analog and digital, but according to the manual it works solely for stereo digital inputs.

Upsampling also works for the L and R front channels in Dolby Digital and DTS.

So the manual is correct?
To ask the question again. If I feed analog signal from my CD player/outboard DAC, am I able to upsample?

I'll try to test it this weekend and report what I find. We've got family coming through on Sunday (relatives of mine who never come to visit, no matter what the occasion, so my wife is determined to make a good impression), so the weekend may be a bit hectic, but I'll give it a shot.

I don't have an answer to the question but why would you want to put the signal through a A/D - D/A conversion? Why not just use the digital input since you would be using the 990 DACs anyway?

I prefer to use analog inputs since I am using a high(er) quality (than 990) outboard DAC.
I am hoping for enhanced musical listening.

But if you upsample you will essentially be using the 990 DACS. Upsampling by definition is done in the digital domain. So in your case using the outboard DAC analog out into the 990 ADC then upsampled and then out via the 990 DACS. If you really want to upsample in the 990 you would be better off feeding it a digital signal straight from your transport.

I use an external DAC (Perpetual Tech P3-A) and it upsamples on it's own, maybe your DAC does the same.