EX - cocking handle thing like on the NF
IX - cocking slide (for example, the Mav would be IX-6 if it wasn't a revolver.)
AS - Air system, simply because is uses air instead of a spring. It probably isn't Asaultsystem, since the Titan only has 1 shot. I'm guessing the RF20 would be AS-20 if it was N-strike (if not RF-20)
V - fires Rocket (already said) BBB would probably be AS-V.3

Rev - obvious
CS - obvious
Also a thought, the E and I in EX and IX could mean external and internal plunger, or something like that, since the scout has a reverse plunger and the NF has a regular plunger.
I wonder how a DTG/Magstrike would be designated...