Although compatible with the AP6522 AP per antenna guide matrix, the better antenna in your situation would be the ML-2452-PTA2M2-036. In regards to the ML-2452-PTA3M3-036 antenna, there doesn't seem to be any preferred way of connecting it to the AP6522, but it has been the norm to use the 1st and 3rd connectors (on the Antenna) to connect to radio 1-0 and radio 1-1 or radio 2-0 and raido 2-1. In previous deployments with a similar situation, one antenna per radio were used, one for the 2.4GHz and one for the 5GHz radio.
Christoph S.