Just one opinion, but I would try to wait a bit and see if something new comes out in the new year. Given the age of the out-going stuff, I suspect(and hope) that Avid have some new stuff in development. Opinions vary, but I spent an hour with the S6 when it was newly released(local GC had a demo unit) and I hated it, compared to the D-Command/D-Control(and never spent any time on the Pro Control). I like the S3 a lot(even better combined with the DOCK) except for the pricing(used pricing makes that much more agreeable)
I can't believe that with Artist Series going away and EOL on D and C surfaces, that we won't see something pretty soon