Hi Jamm,
A general comment on subwoofer "sound": The qualitative nature of the bass you hear from a given design of subwoofer will be determined largely by the position of the subwoofer in the room, the way it couples to the room (and the resulting standing waves that are dictated by the dimensions and shape of the particular room), and by your location in the room relative to the subwoofer's position rather than by the particular way in which the sub generates those long deep bass wavelengths.
Thanks for your comment, semi_on, but a down-firing sub doesn't "amplify" the sound by bouncing it off the floor. All subwoofers couple to the floor on which they sit (it's the nearest surface) whether or not the energy emerges from a front-firing driver, a down-firing driver plus a port, a side-firing driver, or a port alone (a bandpass design where the driver is inside the enclosure, venting its energy to the room through only a port).
It's almost impossible to do controlled testing of subwoofers because of the way each interacts with the room and its position in the room. Every time I've evaluated different subs, it's been a change in the sub's position that radically changes the sound quality, not a different brand or type of design, assuming each sub has roughly the same woofer and enclosure size, and similar deep-bass extension.
Regards,
