IMO that's too small for a pair of 15s. But I do think the external aeros are a good idea. I would say 7 cubes net with 3 6" external aeros tuned to 38 hz should get you a good bit louder.oops haha 15's, i got 2 L7 15's rite now in a 8 cube box tuned to 40 with 2 Zx1000.1's burping a 147.7 at the head rest. im looking to build a box 5.5 cubes with 2 6" external aeros and i want to run more watts to them