A wireless access point (WAP) including: a station grouping module, a transmit selector, a spatial mapper, an output injector, and an input injector. The station grouping module selects a group of station nodes for concurrent MIMO communications. The transmit selector determines whether all station nodes in the group support a multi-user (MU) protocol. The spatial mapper precodes concurrent transmissions to the group using a precode matrix “Q” which spatially separates the concurrent MIMO transmissions to each station node in the group. The output injector injects preambles for synchronizing timing of the MIMO transmissions at the output of the spatial mapper, responsive to an affirmative determination by the transmit selector. The input injector injects preambles before precoding in the spatial mapper, responsive to a negative determination by the transmit selector; whereby transmission preambles are precoded when at least one station node in the group doesn't support the MU protocol.