Call me stupid. What IS/ARE the improvements? I bet there are a couple of them but I also think that there are some downsides that match your positives. Null point IMO.
Not getting too technical on the pros and cons
+=upside, -= downside, +/- null point
XXX
+ better sound quality (who cares he wants an SPL box)
+ uhhhh....uhhhh....?
- more expensive
SX
+/-good SQ (again who cares he wants an SPL box)
+cheaper
+same coil as the XXX
- uhhhh....uhhhh....
Someone smart and experienced with these subs help fill in the other parts. I'd love Mrray, SNova, and Njccbflo to tell me the UPside or improvements to having the XXX for SPL over the SX. I could be way off on everything that I am stating here, but I do not beleive that the XXX is better then the SX if the owner just wants to ad an SPL box //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif