I was not aware that they 450s used to be maid in italy and now there made elsewhere, The ones i have are about 4 years old and i love them to bits, a very very sweet box.
Now about those mackie subs......They just need to make a decent sub to sit under the 450, im not really impressed with the SW 15 or 18 for that matter.
I think a Dual 12" Slam sub might do the trick, self powered, good drivers which can go quite low.
I cant say ive had any experience with the EV SX360, but another powered box i dont mind is the RCF Art300A, nice when your in the right mood, if you get what im saying....
Over and Out