I am not convinced anything can do what you want. You have a audio jack out of the Dot but jump straight to USB in to the Pi. You want the Dot as a front end, can it use a network protocol such as Cast? If it could then you could probably come up with a workable solution even if it won’t be Roon.
I’d say Roon is for everyone as it’s just so much fun to use but you may have to design your system to fit Roon.
Having used Roon from the start, that’s what I would plan to do. Good luck.