My personal experience: I found the biggest jump in sound quality was going from a Mac mini to a dedicated music server/streamer, which at the time was en entry level Aurender. My current server/streamer is an Innuos Zenith Mk 3, I'm using the Innuos Sense music app as I find it sounds better than Roon on the Zenith.
I also have a Small Green Computer, which runs Roon for my Bluesound speakers around the house.
The sound quality difference is noticeable between the Zenith/Sense and the Small Green Computer/Roon in my main system.