What would I do after soldering in the ball valve-I have to connect to the polybutylene pipe at some point unless I want to replace a very long line
You can buy a 'pex x poly' crimp type splice. Poly has a larger ID and has more rings to grab the piping. Or they also have the push in o-ring type. Just make sure its pex 'tan' by poly 'gray'. Manufactured by Sharkbite at HD.