Simple question, best sounding inexpensive DAC.

Cheap ("inexpensive?) involves Just about anything over $200 that even at that point will easily best the Denon changer. There are a buzzillion options in a "just pick one of 'Em" price-point arena.

Now, at the $750 - $1500 price-point strata, the choices now actually provide some quality built and matched quality performance options . Again there are many many options even at that price point.

The REGA Rdac and ARCAM irDac (a What HiFi 5-star rated kit) are just two of the top contenders that are also crowded by the numerous pretenders.

Define "inexpensive" first and then please list what the rest of your gear setup is (system synergy matters big-time) and you may get a rifle approach recommendation instead of a shotgun approach .

The dcs Elgar is the very definition of a bargain.

I like my old Onkyo changer with a Parasound Zdac...

Not sure what your idea of inexpensive is, but a truly inexpensive option would be a Music Fidelity V-DAC (original Black case version). The USB input is not asynchronous, however the coax input would serve you provided your Denon has coax output. Can be had for under $100 used.