From what I can tell, the CC-S2 is the same frame as the CCX(which I have). Im 6ft with a 32inch inseam and have a L(18inch). I was right at the limit on seat tube extension so got a longer seatpost. If I had to do it again, I would have gone with an XL but I liked to be more stretched out/aero on a bike.
Alot can depend on how you want to be on the bike (very upright, somewhat upright or more stretched out/aero).
The L would likely be the best fit. IMHO the M would require another seatpost unless you have super short legs. The XL also might work depending on what you want.