I haven't been real impressed with any of the hertz subwoofers so far , the amps/ componets are very nice ,even though I feel some models are a little overpriced, but for an SPL subwoofer you will probably get more bang for your buck with companys like DD, IA, DC, Atomic, RE,or even the Image Dynamics IDMAX.
I am fimiliar with the shop in Clarksville you are refering to , they are great fabricators/installers , but for SPL I would check around town, for another shop, that is geared more toward SPL monsters , (not SQ, and fab work)