I think it’s possible by using the -s option to create different streams - not something I’ve done, you might be better asking on the Snapcast forum. Post here might be worth following as it looks as though he is trying to do the same.
I don’t know what sort of quality you expect for listening to internet radio in room 2, however as an alternative to separate streams via Snapserver you could set up mopidy on each pi0 in the speaker, then use Musicbox webclient to control the output of said speaker, either radio, you tube or internet archive.
I’ve done it this way for my daughters room, its works well, as soon as mopidy stops, it frees up the soundcard and lets Snapserver back in and vice versa.
There’s a good write up here on the Home Assistant page.
Obviously drawback is that sound quality, through one speaker, is compromised, doesn’t matter to us as I use hive or jbl speakers and my hearing isn’t too good anyway.
I think I tried putting Snapserver on more than one instance and soon removed it as it caused all sorts of problems.