Thank you both very much. I found a (barely, if at all) used ForceXL and have had it for a week or so. Along with the foam plugged SapphireXLs I'm having a ball. I just bought a Radio Shack meter and will do some serious configuring when it has run in a little more. It's sounding pretty good now, though. The hi-fi press makes it seem like integrating a sub is one of the most difficult tasks imaginable!
The system is: a week old OPPO 83SE, SapphireXLs with a ForceXL sub, a Musical Fidelity X-150 and a Cambridge Audio DACMagic handling a fiber optic signal from an AirPort Express.