Your best bet is to pull your modem out of the basement. Have your ISP company move it , thats a horrible spot for Access Point. If you cannot do that have someone run Cat6 in the walls to a spot where you can put the Router within the main living area. The Wifi should be good enough if you pull it from the basement. You can then also get a switch or use the RJ45 connections on the router to run the cable to the Blue Sound once you move it.
Do not use repeaters they are garbage and never work. Repeaters half the bandwidth and you will have drop outs. Even many of the consumer Mesh systems are just fancy repeaters unless they have three radios in the devices to connect. None of that will solve your issue and you might as well just stick with Wifi.
What router are you using? is it your providers? Make sure its the latest as most ISPs provide WiFi6 routers these days. if not get a Wifi6 router.