With just four budget 18's I almost certainly would do they opposite positioning if I ran both sets at once. The Caps would be kept up front. I love the 'wind' effect. The sealed would be put nearfield --- that way they wouldn't have to be run as hard to keep up with the caps -- which can certainly handle more power/volume across the audible board. For those $250 drivers - the price is tolerable and I wouldn't have to sell the caps to rationalize my purchase, which I makes me happy. The caps are awesome for quick grab and go g2g's.
My thoughts on losing money with the Dayton vs. LMS were just this. The Dayton subs in a nice box are just Dayton subs in a nice box. Most guys who buy daytons are happy with DIY flat packs and don't want to pay extra for a nicer box. (heck I'd be happy with flat pack boxes too - I'm not worried about fancy finishes)....But the guys who buy LMS-5400 drivers would typically like a nice looking box to match. (I'm ignoring your wolly mammoth boxes at this junction.
) Anyhow -- I was figuring that since I got such a good deal on the boxes, I could possibly sell the LMS-5400 drivers with the very nice cabs for pretty much what I paid for the setup.
LMS-5400 normally $926 + Box (cost the guy I bought them from $460 each from the cabinet maker that makes Mark Seaton's cabs and he had to buy 16 to get that price) He sold them to me for just under $300 each including my gas cost driving across the state to pick them up. So I figured I could sell the completed ensemble for ~$1200 each (probably) and not really lose anything to worry about).
If you buy four LMS-5400 drivers at once Parts Express charges $879 per driver. four Dayton drivers are $233 per driver.
If the UXL-18's track record has picked up for reliability I still might consider that route. HuskerOmaha confirmed I could swap out my caps for his four UXL-18 for a month or two if I drove them up to his place. In that vein I could hear what UXL-18's sounded like in my room. I've toyed with that idea, for the last month since he offered, but not yet took him up on it. (I think he is a closet cap lover - and this isn't really a favor meant for me.)
I have half a mind to just save a bunch of money and time and sell off the nice boxes. carp already claimed them mid next year if I don't keep them. He has eight SI and one of the most powerful systems I've ever experienced and wants more. This hobby is borderline addiction.