The rock is a great front reg. If you don't want to fiddle with it, don't replace the allen screw with a knob. simple as that.
Volumizers should be easy to find. I know mine was.
The this that will do you best for lowering pressure and increasing efficiency (both will make your kit quieter) would be a spring kit and a valve tool. If you want super high flow, get a Rocket valve or a RED valve. Both are super. If the RAT isn't milled well, which has happened to more than a few people, it can and will strip the inside of your cocker ... not fun.
Back to the spring kit and valve tool ... you idealy want teh lightest hammer (main) spring as possible and you should change valve springs as needed to change velocity dramaticly. After each attempt at changing springs you should do what is called Sweat spot your reg. This is were you slowly but surely raise your reg pressure up until your velocity actually starts to go down. you want your pressure to be right at the sopt that if you turned it either way, velocity would go down. This will give you the best efficiency. Now, if you're under say 30 fps of your target (what you'll be playing at, just turn the adjuster in till you get the velocity. if not. Respring and try again.
You can do this with what ever valve you have now, and you should see a substansial improvement in both voise and efficiency. and all for under $30 us.
it just takes time ...
-Micah