I can’t find any difference between the MAIN and AUX antennas on the antenna description page, thus there most likely isn’t much difference between them.
However, the simplified explanation of the antennas are that the inner two connectors are mostly for high/mid frequency bands, while the outer two are for low/mid bands. I’d recommend connecting the MAIN connectors to the outer two SMA connections.
All 4 connectors are needed for 4x4 MIMO.