DACS are irrelevant if you are using HDMI. The digital to analog conversion would be done in the receiver.
The 500 is using quad Burr/Brown 192Khz/32 Bit Dacs for analog. From the review posted above:
Great pictures then, but it’s with sound that the DMP-BDT500 really excels. Music on CD sounds wonderfully smooth, open and engaging with twinkling high frequencies and pleasing bass weight.
Complex, fast-paced beats are snappy and forceful, while vocals soar and brass solos are easy on the ear. Network streamed music sounds great too, particularly FLAC files, but even lower bit-rate MP3s benefit from the DMP-BDT500’s high-quality circuitry. As we’ve found on previous Panasonic decks the Digital Tube Sound modes lend an pleasing layer of richness and punch. This extra sonic prowess is worth the added premium if you’re rocking a high-end system that can really make the most of it.
As for PQ. I see no difference between the Oppos and Panasonics for Blu-ray, and for DVD scaling, I don't see anything that would make it worth it. Pretty identical. All in all, if it wan't for file support over DLNA, SACD, and DVD-A, I would not have gotten the Oppo (or I would have returned it).