What about the Hsu MBM-12 MkII?? It's a Mid Subwoofer that can be tuned for use with either a true sub or used by itself.
If its plate amp is not your thing, you may want to consider the possibility of modifying the sub to accept a better amp...
If its plate amp is not your thing, you may want to consider the possibility of modifying the sub to accept a better amp...