I assume you are talking about the setting for "LPCM Rate" in the 983H's Audio Setup menu, right? This setting affects the coaxial and optical outputs only, and it will downsample any source higher than the selected rate. The 983H does not upsample.

I don't recall if the 950 handles 96kHz or not (I'm pretty certain that it won't do 192kHz). It's rare to find source material that contains that high a sampling rate and can be played via coaxial or optical. I'd probably bump it to 96kHz just for the heck of it, although most discs you will play via coaxial or optical are going to max out at 48kHz anyway.