Down-firing isn't a special orientation that magically gets rid of higher order harmonic distortion, I think that is overstating that claim. What has originally been claimed is that higher order harmonics generated by the woofer can be partially masked when that woofer isn't facing you, in the same way that if you had a normal full range speaker, and turned it to face the wall instead of your ears, some of its higher frequency output will be diminished. This is because you would only be hearing reflections instead of direct sound, and the higher frequencies are more susceptible to damping. Anyway, the theory makes some sense, however I know of no tests or measurements that back it up. Also, using its logic, the only harmonic distortion that would be lessened is that which can be damped from being reflected sound. Given the frequencies subs deal with, I don't think it will help much, unless you have a sub throwing out some very high order harmonic distortion. In this range of subwoofers, I don't think that will be a problem. Personally I would go for a VTF3, especially at the discount you are getting, I admit to being biased but I do think it is a more preferable sub to the XV15.