Hello, my name is***** to Justanswer! Give me just a few minutes to look up some specifics, I'm working on this now.
I have built radio towers, so I know how RF works. It sounds to me like the GX60 is taking over the antenna. When two broadcasts of the same channel battle, the stronger one wins. If they are on different antennas, you can separate them to lessen the interference.
As I suspected... Your antennas are too close. Your GX60 has too strong of a signal, and is overpowering the GPS signal. You'll need to separate the antennas as far as you can. When broadcasting, the antenna should not be oriented the same direction as the receiving antennas, and should be as far away as possible from the receiving antennas. Remember, when there are two RF signals, the stronger one wins. They do not mix, it's one or the other that will be received. That is why you're losing your signal. The GX60 is taking over the airwaves, stronger than the signal that needs to be picked up.
Hmm, something with the electronics has gone haywire. Replace the GX60, and see if that fixes the problem. Since the other equipment works without the GX60, I don't think the rest of the system is bad. It sounds like a resistor in the unit went bad, causing it to output unusually high RF, which interferes with the antennas.