Re: New PVC piping attached to old broken copper pipebath fixtures...help!
on the shower valve itself you will need to make the transition to a THREADED fitting. The reason is this is how you are going to go from the valve to the CPVC. The CPVC has a MIP and a FIP adaptor with brass male/female threaded parts in the fitting itself. MAKE SURE TO USE PIPE DOPE. I recommend Recto SEal #5, and it is a yellow paste that will firm up, unkike straight teflon dope.
Now here is the kick. The shower valve may have only sweat connection. And if you sweat the joint without taking out the valve cartiidge you will warp it. Also, if you don't know how to sweat copper it may be a problem. I have seen ALOT of plumber mess this part up in both residential(custom baths) and commercial(hotel). You really need someone who has done this part before. I will compare it to the first time trying to fix a flat tire on the side of a very busy road, at night, in the cold, in the rain. But, once you do it you will say "oh, that was easy" and think nothing of it.
Process of elimination. Good luck.