Hmm... Fell foul to a similar limitation when trying to move to Spotify instead of Amazon Music. You can't stream to Spotify music to multiple Echo devices at once (ie: all playing their own steams)... So the only option is Amazon MusicI have the Echo Gen 3 as stereo pair and it sounds pretty good to me. I'm not an audiophile though, so no doubt it's a shocker to proper ears.
No, the BBC decided to prevent access (from the UK only mind) to all of their stations through TuneIN, which worked fine with Echo stereo pairing. As above; BBC Sounds skill does not support the Echo stereo pair feature. What a crock eh. The reason claimed is under the guise of wanting to better understand listening numbers through streaming which was unavailable from TuneIn
Bit of a kicker that anyone outside of the UK can continue to access BBC stations through TuneIn!