Just to be clear; with MR76 you could use different antenna types, to provide different coverage areas for 2.4 GHz and 5 GHz, because each radio has its own pair of antenna posts. That is a fairly unusual requirement though - but I have seen it, occasionally with (say) wireless mesh; directional antenna on one radio (2 posts), in one band, for the backhaul, with (say) ANT-20s for local clients on the other radio. In that case the client connectivity would, essentially be in a single band only.
This differs markedly from MR86, where all 4 posts are connected to BOTH radios; for which the connected antennas must be dual-band and must cover the same area.