Can I use two 4k displays with MacBook Pro MGXA2
Multiple (up to 12) thunderbolt displays or devices can be chained and utilised by a single port. Whether your device has the power to do this, and whether the OS allows it is a different matter. Your device should be running Mavericks or Yosemite and should be powerful enough to use the monitors. With most Thunderbolt Displays they can be plugged into the mains and therefore work fine in chains with low powered devices.