So your internet service is DSL, which may be your problem. What internet speed do you get, and what resolution music are you trying to stream? My neighborhood has very old phone lines, and when I had DSL service years ago, I was only getting a maximum speed of 5 Mbps (often less).
When you use the music streaming app directly (e.g. the desktop or mobile app of Tidal or Qobuz) without Roon, do you still have streaming issues? If you do, the problem is probably the quality of your internet connection. Roon is a special case because it is especially demanding about needing a good local network (e.g. wifi).
BTW, where are you located? There were multiple recommendations for Fritz, but I was surprised that I had never even heard of the brand. It appears to be based in Germany and not sold here in the US (likely not certified by the FCC).