I'm not sure I'd bother with the Klipsch subs even with that deep of a discount. Glancing at the specs, it looks like the THX subwoofer line delivers massive output, with 130dB at 30Hz, 122dB at 20Hz, and 112dB at 15Hz. However, it's worth noting these numbers are spec'ed at 1m, with two subs side by side, in 1/8th space (i.e. corner loaded). To get this number closer to an apples to apples comparison with 2m ground plane numbers we're used to from Josh, you'd have to subtract 6dB to drop to one subwoofer, another 6dB to go from 1m to 2m, and another 12dB to convert from 1/8th space to half space, for a total of 24dB to be subtracted. What you're left with is 106dB at 30Hz, 98dB at 20Hz, and 88dB at 15Hz, which aren't terribly impressive against a sub like the VTF15H.
As you say, there's more to life than quantity; however, given the VTF15's measurements and configuration options, I don't see quality being a problem either.