The DACs in something like a Denon 4306 or Onkyo 875 for example leave an awful lot to be desired. You gain HD audio format, but such a massive amount of detail is lost passing through the AVR (not just DACs but also DSP etc) back onto the AV9 again that you have lost more than you gained IMO.
However find a Blu-Ray player with decent DACs and internal decoding to analogue outputs and you can feed your 7.1 MCH input on the AV9 directly. We have plenty of setups using Zektor switches from BD, HD-DVD and SACD MCH outputs all into the AV9 and they sound better than any currently available HDMI based solution (excepting the Lexicon). The Sony 300 and Panasonic BD30 have good DACs on their MCH outputs, but don't decode all the formats. The Panny decodes all the lossy formats and just leaves DTS HD MA and Dolby True HD which is as close as we can get so far. Nice player too IMO. A perfect stop gap for a year or so until the technology is out of infancy and some decent products from decent manufacturers are available.
(I won't go on to the limitations of using HDMI interface to send audio in the first place! It's been more than covered)