Oh, and improving sound quality…
My guess is that what you’ve got now, with respect to Roon and the TX-8250, is just fine. There’s a lot of mythology about “outboard DACs”, and there are lots of people here who like to fiddle around with them, but the built-in DAC in your Onkyo unit is up to handling the task with pretty good fidelity.
Generally speaking, the biggest improvement most people can make is better speakers and adjusting the speakers to the room they’re in. Roon can help with the second part, and there’s lots of advice on this forum about the first part.