6V LDO regulator for 6A peak motor
Do you really need to add a 6v regulator? To quote from the specs of your motors (my emphasis) - "These motors are intended for use at 6 V. In general, these kinds of motors can run at voltages above and below this nominal voltage, so they should comfortably operate in the 3 – 9 V range, though they can begin rotating at voltages as low as 1 V." Sounds like they'll be quite happy with the 7.4V