Rhl Jazz-
The sub you have is the Continuum 12SW. The box is not MDF but an industrial-grade particle board that most cabinetmakers don't like to work with, because it is much harder to cut and shape than MDF. MDF is a weak wood, and to make it strong enough for woofer/subwoofer cabinets, it must be quite thick, ala Thiel, or combined with other woods, like our Continuum 3.
The 12SW you have is still, by anyone's standards, a really good sub- far more linear that what is out there for sale nowadays. It was reviewed in December 1999 Home Theater Magazine.
If it were my $$, I would hang on to it, and contact me for information on how to obtain the proper crossover to make it blend with your B&W speakers. This is not hard.
We sold that Energy crossover to a few customers (we bought them from our local retailer), because it had the correct filter slopes (Model EAC-1, no longer made), and because it was inexpensive. However, we always informed the end user that it employed not-so-good sounding op-amps for the signal to the main speakers, thus compressing the soundstage and dynamics, and sounded somewhat electronic. But it did blend the sub to the mains properly. Although it was marked for "stereo sub amplifier out", it was most definitely a mono sub signal, FYI.
Best regards,
Roy Johnson
Green Mountain Audio