LHP2017,
To answer your question, yes. You should be talking to both, but the ultimate decision is with the HC. There have been many threads over the years on HSBBWeb about recruits dealing with their possible future position coaches and not the Head Coaches only to find out the position coach and the HC were not on the same recruiting page. The pitching coach is your "champion" but the final decision will be made by the HC.
As a follow up to your recent visit, I suggest you reach out to the HC and tell him about your interest in the school, and your conversations with the PC. This was a lesson my oldest son learned at one of the schools that would eventually offer him. About 5 minutes into his first conversation with the HC in his office, he learned the young and inexperienced PC had not been keeping the HC updated.
Good luck!