Budget RPI Upgrade Suggestions

I would start right here. A guide how to do room correction and use it in Roon

It’s a big subject, spend a bit of time experimenting for free and trying a few things. All you need is a umik-1 and free software. Later there are paid options for more advanced software or people to do some if it for you. But I think it’s much better to experiment with rew and read a bit first so you understand it a bit more and find out what your rooms like and more importantly what sound curve you like.

Start as simple as you can as it can get complex but it doesn’t necessarily need to. Plenty of advice here esp topic above, and other forums.