PACX and FS2Crew can run together just fine. It’s just a bit of a hassle that I need to keep going back and forth between apps to manage passenger announcements in PACX, and keeping my cockpit communication in FS2Crew.
That being said, if I want to fly a flight with a custom boarding music and safety announcement, I would run both PACX and FS2Crew. Otherwise, I just run FS2Crew since it has its own basic boarding music and safety announcement.
Just a note, the FS2Crew only works on FlyByWire A32NX aircraft, and sometimes I use it on Headwind A330-900neo. I don’t have any other aircrafts installed in my sim, but I don’t think FS2Crew will work on other non-Airbus aircrafts.
Pacx on the other hand, works on any aircraft you fly.