There are 3 x 3 panel configurations selectable but appears none provide COM2 capability. It seems that all the various GPS and the lower panel GTR225 adjust or use Sim internal COM1. (And NAV1 for that matter).
Every config has at least a single Garmin GPS so I would suggest make primary GPS COM1 and the GTR225 as always COM2.
In the case where there are two Garmin GPS I would suggest they use COM1 and COM2 and NAV1 and NAV2. Would it be possible to remove the GTR and the standalone transponder in the two GPS case? Not sure if anyone would have the 4 Garmins
The Push action of the GTN650 knob is not assigned correctly - should be switch between showing COM and NAV freq.