I've done some investigation. The new Planet Rock web player uses a proprietary Flash protocol called rtmp and users of other media devices such as Sonos have also lost the streams.
However, using SqueezeCenter (Slim Server) I have found a stream that is still working on Soundbridge players: mms://venus.radica.com/planetrock
Also just noticed that another stream for PR has been recently added to RokuRadio and can now listen to the station. Thanks.