Can i point out the G91 is capable of upsampling two channels only. If the source is a CD, or two channel dvda/dvdv it will upsample on the main output to the max rate specified in your settings. If you specify the preamp analogue out as the Application it will automatically upsample to x4, so CD's will be upsampled from 44 to 176kHz.
In Surround mode the upsampling is disabled as the G91 is busy handling base management and speaker delays.

Hope this helps