You have n SPL meter, REW and that mic act as an SPL meter, no need to buy anything else.

Are you planning on using just the Axiom 5.25" drivers in that size of box? I don't believe you are but I thought I would ask. With that size of box you are well on your way to building your own VP160 (pretty much the same volume) with 2 6.5" drivers you buy from Parts Express to go with one of the 5.25 Axiom mids.

You should call Axiom and see if they can supply you with the impedance curve for the tweeter.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70