Yep, got a 24 inch cube with two 18" PR's (from Stryke). The deal w/PR's is you need approx. 4x the displacement from the PR's compared to what the driver is capable of. Dual 18" high excursion PR's will give you that with the 1503, dual 15" PR's won't.
Sealed subs have better bass for music, assuming it's a low Q design (ie, the box is sufficiently big). But there's really no way for a sealed sub to keep up w/a PR or ported box in the very low bass. Mine's tuned to 16hz, and even with LOTR above reference level, I've never bottomed my sub. For movies, I really prefer the ported and PR style subs, as the bass is a little more "present", which I find I like. For music, I still like sealed subs best with one exception - the VMPS subs are the best box subs I've heard, and they use a PR on the bottom. Don't know how brian does it, but they sound awesome with music.
Haven't heard Jeff's sub, but he's heard mine, perhaps he could comment. . .