My Denon DVD-3800 BDCI has the high-end DAC Burr-Brown 1792. But these days I mainly stream ALAC files from my iPad to my Denon.
I think the DAC in AVR are so good already so I don't think an outboard is necessary.
I think the DAC in the $500 Outlaw 975 pre-pro is also good enough for anything.
I agree with you if your needs are just playback.
I think a DAC is useful depending on what else you want it to do. I use my DAC a lot, because it has useful mix ability, phantom powering and excellent on screen settings, and good memory functions, so you can switch from your settings for analog versus digital inputs in a second.
So I think you get a DAC for what else you want it to do. If this is part of a computer system, like mine is, it is the DAC for my audio workstation, then you might as well maximize facilities and options, with good on screen functionality.
A DAC should be selected if you really need one, and choice comes down to facilities, good ergonomics and well though out designed and implemented software. That is why the DAC I selected is so popular. You seen them everywhere.
I guess pictures are worth a thousand words.
The DAC is the blue unit above the computer/audio workstation.