hmmm no, I don't believe that the LMCE control of SqueezeCenter allows for splitting of streams so that they remain synchronised... sync is quiet difficult at the best of times, but if LMCE doesn't have full control over the output devices (which it really doesn't, SqueezeCenter controls them albeit on a LMCE machine) its going to be impossible unless SqueezeCenter itself supports synchronised playback, exposes that functionality to the TCP control port, and the slimserver-streamer plugin for LMCE supports that functionality (which it doesn't currently)... lots of ifs followed by a no.. sorry!
Even with MDs it is difficult to get perfect sync - the only realistic way around this is the xine-server/client model I proposed recently, which would allow for at least broadcasting possibly even multicasting, either of which would immediately solve the sync issues with MDs. However, that is something outside my capabilities to implement and is not high on the list of priorities for the devs, currently.
Streaming Internet radio, as I say, is currently not supported by the slimserver-streaming plugin, however there is nothing stopping you configuring the individual Squeezeboxes/softsqueezes with presets for the Radio stations you want. They are perfectly capable of playing Internet Radio without LMCE's intervention. However, again, sync will be a problem, primarily because you cannot guarantee what buffering is involved. These protocols simply are not real-time. Again, the only way to ensure this is to have LMCE pulldown and buffer the stream itself, then use a realtime broadcast or multicast to get them to the end points.