A few thoughts come to mind.

First, Burr Brown DAC's do not instantly translate into better sound. They are but one piece of the puzzle, and there are a number of other companies around that make equally good or even better DAC chips. When comparing the Onkyo 885 to the Model 990, I found that the 885's Burr Browns didn't give it an audio performance advantage over the Model 990 (even with Audyssey in the equation).

Second, there's more involved than just DAC's. The 886 has a better video processing section than the 805, both due to the chipset used (Reon vs. Faroudja) and the control available (ability to bypass the Reon for some inputs while applying it to others).

Both the 886 and 990 should run cooler than the 805 because they don't have amps in the chassis. Even though you aren't using those amps, the receiver will tend to put off more heat.

If you are talking just about sound quality, I wouldn't expect either unit to be a really big upgrade over the 805.