For a HX machine the simplest PID's work well - you're not trying to micro-manage temps like you would with single boiler machines. I prefer Watlow or CAL Controls because of their more robust builds, but I only buy used controllers and the cheaper Auber models should work just as well for this application.
The PID's built-in relays are seldom rated for the high amp load a heating element requires, so I advise using a d.c. switched PID & a SSR. You'll only need OT1 to manage the temps unless you opt to use OT2 as a hi-limit switch. Putting these together is easy, so just follow your instincts; and use the auto tune function to set it up.
Wire the heating element circuit directly, as though you wanted it always on. Then cut one of the element leads and connect to the output of the SSR. The SSR's output is now the switch that turns the element on/off. The PID turns the SSR on/off by energizing the SSR's input when the thermocouple senses a lower than preset temp.
I like to mount the PID in the front panels of the machine (requires some clearance behind the panel). The PID's I favor are 1/32 DIN size-factor and require a 7/8" x 1 3/4" opening. If you don't feel like chopping into the front panel, the PID can be mounted in a separate enclosure, commonly mounted on the side of the machine.
