I run 90 PSI on my J325. There's an interlock to stop the machine from operating without correct air pressure.
It sounds like you may need to clear the Z limit switch. Is the quill retracted so much that the bottom of the ground surface of the quill is higher than the chrome plate that bolts onto the underside of the ram? Or is the quill extended quite a lot? Behind the quill you'll find a round steel disc on the underside of the ram. There's a hole in the middle of it and a 5 or 6mm Allen wrench will stick up into that and engage a matching socket in the bottom of the ball screw. Then you can turn it and move the quill off the limit switch.
I've never used the Dynapath control so I don't know how to advise you on that. It will ask you to home the machine. There are arrows on the front of the table and the carriage that let you center the table for X home and there is a sheetmetal arrow on the right side of the knee that you align the front edge of the carriage with for Y home. Having the bottom of the quill even with the chrome ring is Z home.