Depending on the shape of the box....i think kicker recomm. a 15x4x14 port and suggests you can fold(turn) the ports against the back walls if needed and shouldn't be done with round ports.i wouldn't "think" that 4x 6" round ports would give a good tune to a box that size BUT this is just my 2 cents mind you. good luck though and what are you using to power the X ?Would 4 6" ports be enough for a solox 18 in 10.8 cu ft gross?