I don't think that there's much floating around these parts on
Deep Sea Sound, so I'll give them a bump here. The company's current offerings are built around Stereo Integrity's
HST-18 and
HS24 drivers, with power supplied by a 4kW SpeakerPower amp. As you might gather from that, the subs aren't exactly inexpensive. Also, given sheer size and enclosure requirements for the HS24 driver, the flagship offering isn't what you'd call compact. However, given the measurements conducted by Josh on the raw drivers, it's fair to say these two, and especially the 24" monster, are ULF champs. As for the cabinets themselves, there are several veneer options, as well as the option for an end table sub:
I was hoping to hear these at Capital Audiofest this year, but David Gage (the company owner) had to pull out since the show planners weren't going to let the subs even stretch their legs.