The Toshiba HD-A1 and XA1 HD DVD players upsample all internally decoded audio to 24-bit/96kHz. Does this really make an audible difference?

The 990 has that option too with the UPSAMPLE command. I haven't heard any improvement over BYPASS, though I can hear an improvement in going from STEREO to BYPASS, or at least I think I can. Maybe if I had the ribbon tweeters of the Magneplanar 3.6 UPSAMPLE would make an audible difference, but with my 1.6QR's - no. What I mean with all this is that whether suchandsuch change makes an audible difference depends on the capability of the rest of your system, among other things.