Sorry but I don’t understand the OP. When you use the TuneIn option on the Browse menu on Sonos, TuneIn acts merely as a URL lookup service; Sonos fetches the URL directly from the station, not using the TuneIn service.
@goeatwhatever - the only ads you should hear are those on the station’s own stream, which are surely there in whichever way you access the content? There should be no ads from the TuneIn service itself. Which ads are you talking about?
I have been using the ‘TuneIn’ audio source to listen to radio on Sonos for 10 years. I have no TuneIn account (neither free nor paid) and I am yet to hear a TuneIn ad. The problem with taking an aggressive tone in a rant is that there is always a risk that one turns out to have been totally mistaken.
Depending on what type of controller devices and speakers you have, you may be able to log into your paid TuneIn subscription on a mobile device and use Airplay or Bluetooth to play to your speakers.
Which other audio system are you planning to switch to?