Any recommendations for a subwoofer driver?

I have a pair of ADS L1590's in my HT system. Recently I purchased an older pair of passive ADS subwoofers that esthetically match the L1590's very well. I want to use them because they look and fit my system well, but they are missing the original 10" drivers. I want to install a driver that will improve on the originals, but don't know where to start. They are a sealed enclosure and measure about 2 cubic feet internal volume.
Parts Express and sells raw drivers amoung others. Do you know anything about Theil-Small parameters?
Flip, if you are looking for a reasonably priced 10" woofer designed for used in a sealed box, Audio Concepts Inc(ACI) would be a good place to go. While traditionally a company that catered to the speaker hobbyist, their line of audiophile speakers(ACI and Dzurko[sp]) are held in some regard.

If you are looking for a more expensive driver, Dynaudio has been the other choice for this alignment.