I'm not suprised, audio levels for TV in general are all over the place. I have the same hardware as you, however I run my HDMI connection straight to the TV with an optical connection to the 805 when I want to listen to the DTV audio through my sound system (TV speakers are fine with me for most shows that I watch).
I do not think that DTV has much control over the audio level it transmits; depends on the source providers.
One other comment, remember that Reference Level only refers to the level that movies are mixed at, and the level they should be on DVDs and Blu-rays. For other materials (CDs, TV, concerts-even on Blu-ray) you just never know what you are going to get.