Since my google-fu is strong I was able to figure out all your abbreviations.
Anyway the Folding stock system only works with the Rock River Arms PDS piston driven system vs the PWS Primary Weaspons System, PDP piston driven pistol or PDR piston driven rifle. The PWS gas piston system uses a more std. type bolt carrier that when cycled extends out behind the lower receiver and into the buffertube, precluding the ability to side fold. The RRA Rock River Arms system uses a special bolt carrier which does not extend out the back of the receiver durring the firing cycle. Also as per Rock River's website the current gas system they have developed is not to be used with silencers.