I don't know whether or not this has any bearing on the issue but in checking the specs of the 772, everything out of HDMI is processed via PCM. I have a BDP83 and shortly after I got it I experimented, in stereo only, with both the analog and HDMI connections to see how they would compare. Both were pretty similar with the edge going to the HDMI connection with a slightly stronger bass. There wasn't the sub issue that has been described. With standard DVD, of course, from my experience and as JohnK noted, the AVR will automatically downmix to two channel BUT it shouldn't affect the bass. I can't really speak for the new lossless codecs because I have never tried it, however, intros to Blu-Rays, like standard DVDs, are usually two channel only and it still shouldn't affect bass reproduction.
In the end, the AVR takes its lead by how the player is set up. If your sending everything out bitstream(via HDMI) then the decoding, speaker levels and LFE set-up would be all done thru the receiver and obviously that is the way you want it. As you know, the BDP83 has the excellent simplified start-up wizard which makes sure everything is the way it should be especially making sure the HDMI connection is in the "advanced" audio mode. That might be worth another look.
