I've followed this saga for a long while, and was sad that Radium had stopped streaming Sirius XM channels.
On a lark, today I tried again today, after creating a new Sirius XM streaming account. And here's some great news: it's working fine! I was able to log in, I was able to search for channels, and I was able to select and play any channel. It's working right now on my 2015 MacBook Pro running macOS 10.14 Mojave. I'm streaming Sirius XM channels via Radium 3.1.3. I didn't have to apply any hacks or tweaks. It's just working. So y'all may want to try it again...
Also working for me! Not sure what's going on, but certainly not going to complain.
Edit: Have noticed that it freezes after selecting a station, and takes ~80% of CPU resources as per activity monitor. The music keeps playing fine though.