I am a sceptic for two reasons...
1) As Don points out, the digital to analog stage is more than a DAC chip, so to test the DAC chip itself would be hard (I found one person online who tried to do it, and one person is not enough to get a lot of info, and he only tested a handful of chips, which are likely NOT the ones used in current models)
2) I have found very little on the internet regarding objective tests of ANY DACs be they a chip or a product ( I was amused by one product which was over $2000 and that did not include a power supply...wow)
So I can only conclude that any statement about whether DACs make a difference in sound are hard to back up. I don't see people trying to prove it either, to their credit. What I have seen is people who said they compared DAC products, which are more than just a chip. That info is not useful when discussing the DAC chips used in receivers for reasons Don already covered.
That leaves me with one conclusion...it's pointless to concern ourselves with the DAC chips used in receivers (in the face of the knowledge I currently hold..with new knowledge I could change my mind of course
As always, I feel that time is best spent elsewhere. Perhaps learning how to use software to analyze your room response and considering bass traps...perhaps better/different speakers, a better sub, or simply playing better mixed music or better mixed movies