I have several (5) S series speed sensors for all my bikes, but teh S series monitor itself is on its last legs and I fancy an upgrade to the latest and greatest polar have to offer.  I think this is the CS series (CS600/CS400 maybe?).  But I note that the chest strap (transmitter) is not compatible and so I'm doubtful about the speed sensors also.

 has anyone got any experience of this or can give me info on the compatibilty?