I think I may have the answer, Keith, but it will take a call to Pyramyd or someone to verify. The S16s is the shrouded version, and I think it's made in a couple of different variants, one for the European market, and one for the US. I also noticed that PA's site is advertising the S16, no small "s", so maybe there was a legal issue? I believe the original S16 was unshrouded, more like a Talon with the barrel sticking out of the frame. It gets even more confusing, depending on what you read where; some sites say detachable, modular shroud, some say integral shroud.
I'd be interested to hear what you find out, this gun recently ended up on top of my "next gun" list :-). I love my Talon SS, but a repeater is starting to be more interesting. Noise level isn't a deal breaker for me, but quiet is nice. Later.
Dave