I can't believe that all three are supposed to be "official" continuations of the show. I mean, I agree with mscbryk, in that they don't really gel together.
From what I gather, the new CD series is supposed to take place sometime between the end of the original show and RtC. I personally like to think that it's sometime during the late 70s or early 80s that this stuff is happening. I mean, if I had to put a time frame on it.
RtC could be a continuation, and COULD gel with the newer CDs. I mean, if the new CDs take place in the 70s or 80s, and all is well and good, or at least STABLE whenever the series ends, enough time could've passed so that the stuff with RtC takes place. I'm not 100% on this, because I haven't listened to RtC in a while, and I've never even heard VaC so that's just my speculation from what I have heard and do remember.
As for "The Salem Branch". Well, is there really much I can say about that? I mean, if we consider that canon, it's in a world all it's own. Another branch of canon. I prefer not to consider it canon. The Marilyn Ross books were never considered canon, and as far as I'm concerned, any other books written in the world of DS aren't canon either. Except for maybe Angelique's Descent because it mostly chronicles things from Ang's POV.