Converting I+ I- thermostat to 'standard' wiring
You should be able to wire your thermostat to the conventional terminal block on the air handler

If you look at the bottom edge of your air handler's control board, there is a terminal block to the right of the two ComfortSync connections that has been labeled with conventional thermostat signal labels.  This means that your control board should support standard 24VAC thermostat signals instead of a communicating thermostat.  You can test this by disconnecting the communicating thermostat from the rest of the system, then jumpering R to G on that right-hand terminal block; when you do this, the fan should come on.

If that is indeed the case, then I would wire the new thermostat conventionally, as it sounds like you have sufficient spare wires in the cable from the air handler to the thermostat to do so.  You shouldn't need to touch the wiring between the air handler and the heat pump, by the way, for that matter.