Taking your second point first, I have a premium subscription to ClassicalRadio. As noted, it does not have a Sonos app. The workaround is to load individual channels through TuneIn, as the ClassicalRadio/JazzRadio sites note. That's how I have several channels configured.
Now I have no way of knowing what the stream is - it could be the 320K high rate setting you could get in your browser with a paid subscription. My only point was, some services - and I cited Pandora specifically - don't give you the premium rate on a third party hardware device, even if you are a paid subscriber, as I am.
A slightly dated grab from Pandora's support pages: "Pandora on the Web plays 64k AAC+ for free listeners and 192kbps for Pandora One subscribers. All in-home devices play 128kbps audio, and mobile devices receive a variety of different rates depending on the capability of the device and the network they are on, but never more than 64k AAC+" .Apr 1, 2014
s.
Edit - And let me expand on this a bit. Sometimes you don't get premium audio, even when you're getting premium audio. I subscribed to Slacker for a while, and even though it offers a premium bandwidth of 320k I wasn't getting more than 128k on the classical and jazz channels I listened to. After a little back and forth, a Slacker rep told me that not all channels will stream at 320, and if I recall correctly, third party hardware was limited as well.
i canceled.
Edit, edit - In fairness, Sonos now says a paid subscription to Pandora gets you "higher quality audio" though the wording is a little tricky. And Slacker's Sonos page says it streams "thru http" at 320, though again I'm not sure that translates to 320 on a Sonos, or 320 on all Slacker channels.