You're limited by the Horsepower of the system..
You have 2Hp.. that does the 2.2gpm @ 1200psi nice, ..but 4gpm would drop you to about 500psi.
Also.. You need to match the RPM's.. look at the motor RPM's to match a Direct Drive pump.
Call me for the pump & options.. You'll be Glad you did !
..and those skinny 3/8" pipe coils don't like 4+gpm.
Call me from next to your machine, and I'll explain your options