Totally with you on not needing to or waiting to dig up your floor to lay cables, obviously that normally solves any networking issues instantly, but it's not always practical retrospectively nor should it be an absolute requirement. A well configured modern WiFi network
should be fine for streaming.
My point was that
newer devices often default, or may indeed
only connect, to the 5Ghz channel of a dual band (2.4Ghz/5Ghz) router / access point and that the 5Ghz band often has more trouble penetrating though walls to the other side of your house, either due to the nature of the 5Ghz waves or interference from neighbours on that band. Hence why older 2.4Ghz only devices like the Connect might work better in that room.
If you have tested that both your 2.4Ghz and 5Ghz networks are solid and uncontested (ie. your neighbours aren't using the same WiFi channel as you on either band) then I guess something else is at play.
But that fact that you has issues with both Roon (admittedly Roon is very network heavy) and the BlueSound suggest that your WiFi (possibly just the 5Ghz channel given that older 2.4Ghz devices like the Connect seem to work fine) might not be as solid as you think.
But if you're sure your WiFi is solid (via an app like
Netspotapp or similar) then I guess it's just going to be a case of trying different devices til you find one that works with your network.
If your WiFi network is solid then I'm guessing you had similar issues with the BlueSound when it was placed near to your router / access point?
Your repeater is possible a bit of a red herring as the repeater itself (unless hardwired) will still have to make a WiFi connection back to your the router / access point itself, so will equally suffer from a poor WiFi network.
Just trying to be helpful..... I couldn't care less about any particular device working or not working, not do I think you should need to dig up your floor to lay cables. But what you describe sounds like a WiFi issue or a faulty unit — otherwise people would be sending their BlueSound devices back by the truck load, which doesn't seem to be the case.