I'd like to put the enclosure design into another thread to keep this one on point. So with that in mind, I'll sum up the thread here, and move on to designing a better enclosure. Regarding the problems I was having with the AE speaker, and my request for other subwoofer recomendations:
It looks like the SDX15 and Tempest-X are good recplacements. They seem to have similar performace and pricepoints. When modeled in ported 9 to 11 cu. ft. enclosures, they all seem to model well and perform similarly, although the AE did not have the flattest response. When modeled in ported enclosures from the 6 to 9 range, the the AE seemed to do better on the low end.
As far as the original problems with the AE driver, it looks like the OAudio 500 amp is NOT a good choice to power it. The amp was fine on another sub of that size, but caused clipping early on for the AE driver. My guess is that the lower resistance of the AE speaker was the culprit. Running the same driver on a single channel of the Behringer ep4000 produced great results.
Thanks again to everyone for their support an encouragement to give the speaker another chance.
Now, onto creating a build thread for it...