IMHO, HDMI.  However, there is much more to the setup than the connector and it will also depend on what your receiver is and can do.  

Finally, you should try both ways for yourself as I do not see the general choice as black-or-white.

Kal

What Kal succinctly said. Also, there are a lot of settings and considerations - got to read through the manual. Yeh I know it's about 100 pages but u need to. 

I suspect that the best sound quality would be from running cables direct from the analog outputs to the receiver, but you can certainly compare this to an HDMI connection and evaluate the sound.

The tech guys at OPPO are very knowledgeable and helpful and will talk with you about this if you call OPPO. The pnone number is in the manual.