When I remodeled my master bath, I added several "water features" in the shower. There is a main temperature control valve (thermostatic valve). Then there are on/off valves for each item: overhead rain head, handheld sprayer and body sprays. The thermostatic valve had several "out" lines, well check the picture and maybe it will be more clear. I agree on the PEX, it is awesome stuff and beats having to solder all those joints for sure: