I never could hear any difference that way as opposed to just letting my 7703 handle everything.
YMMV
I completely agree that the subtle difference in adding an external DAC would be swamped by the enormous potential benefits of the 8805's room correction and/or subwoofer integration.
I believe that RichB was on the right track when he mentioned that the 8805 (as well as most modern AVRs and processors) is a network-centric device. I think the correct solution to getting the best sound out of the 8805 is to feed it a digital signal. There would be no need for an A-D-A conversion. These D&M products have at least two options for playing Tidal that don't require an external DAC or the use of HDMI inputs:
1. Use HEOS. The free HEOS app controls the 8805's built-in HEOS streamer. It allows you to play Tidal and Spotify as well as your own music stored on your home network. I've tried it and it works great.
2. Use the coax input. Build a cheap Raspberry Pi streamer by adding a coax output board such as the Allo Digione or the HiFiBerry Digi+ Pro. Using Volumio with their new subscription service you can now stream Tidal. Another option is Moode Audio which lets you stream Tidal, Qobuz and Spotify.
Of course, in both cases you would be using the non-MQA DAC in the 8805 so there would be no MQA capability. However, since MQA is of very questionable benefit I don't think it's anything to worry about.