The FSB (full shroud barrel) is the newer release from HW. The Beeman (that's shown on PA's website) has the mod on the end of the barrel. I'm sure it's glued on and non-removable, but most manufacturers are going to full barrel shrouds for the US market. Mod thingies on the end of the barrel (even on airguns) are a touchy issue here. I have no idea which is the quieter of the two. A properly done full shroud can be very effective. The Maurader is alleged (I say that cause I have never heard one fired) to be one of the quietest PCP to date. For me, personally I would opt for the shrouded barrel. But that's just me.
Nathan