Originally Posted by bakerwi
There is no difference just preference.
^^ As I said before upsampling is rather like oversampling in modern DACs, for the benefit of higher sample rate going through the filters. The short video on the CA website explaining the upsampling is a bit misleading, as the bloke talks about more information of the upsampled audio when in truth you can't add real information to the source, just as in upconverted video.
The difference between CA and Oppo in design is more than just the oversampling. Without the option to turn it off you just don't know how much it contributes to the SQ difference. According to Nyquist there should be no difference.
Originally Posted by Barney1
I guess I can just try each one L/R and see what sounds better.
That's a meaningless or pointless comparison because the rear surrounds are derived mostly from the side surrounds in the original 5.1 theatre mix. Every mix is different and depending on the contents there may be a lot or little difference between the two. You wouldn't normally compare the front R and L and see which sounds better.
If you just connect either one you only get half the info. There is a proper way to MIX the two together (not with a Y-cable) to form one channel. Or else just forget about the extra channel, set the player for 5.1, at least all the info is preserved. When sent digitally of course all 7.1 can be sent intact.