I am SURE i cant go wrong with the 2 larger SVS offerings, but just like how you wouldnt get a estimate from one plumber/contractor i dont want to just jump on the SVS because a guy at SVS recommended it.
It's like this
Sub A is a sealed design. Below a certain point, the output falls off at a 12db/pctave pace.
Only the driver produces any sound for sub A. The internal volume of the box affects the behaviour of the driver especially with regards to its ability to move in and out and reproduce the deepest bass.
In sub B, a vent acts as a helmholtz resonator to produce sounds
below the capability of the driver (in conjunction with the rolloff of the driver above). This will produce deeper response. IN effect, not only does it need its own space (vent space) but it needs its own internal box volume as if it's a driver. It's sharing it with the driver so the internal pressure would create too many issues in response if you just used a small box big enough for the one driver. After a certain point, this port's output actually works against the driver and produces a sharp falloff in output (24db/octave) but usuaully we can push this point a lot lower than the equivalent point in a sealed sub.
So the sealed sub might still give you output around 40-80hz, but you likely won't get the deep bass wIthout heavy EQ, which usually asks a lot of an amplifier and driver and usually just limits your output everywhere to keep things on an even keel.
For music it's usually okay, as only a few instruments extend much lower than 40hz or so. In a small room, the added energy of reflecting the large wavelengths will give you back some of the lost bass below the "knee". In a large room this energy can spread out a lot more and won't reflect as much.
For movies however, we cane easily have content down to 15hz or so. Heck, Black Hawk Down IIRC has content down to 8hz. Reproducing this extreme bass obviously requires many huge drivers EQed or huge drivers and huge ports. Either way it's never going to happen with one small driver in one small box.
Usually at your price point you should expect to be reproducing down to around 22-23hz with meaningfull output and good sound quality. If you're only getting down to around 35hz in your room, then you're pretty much missing a full octave of bass! An octave where movies in particular THRIVE and really dominate!
WIth all that said, perhaps a passive radiator option might be in store for you. Think of it as a ported box, just minus the port volume I mentioned earlier (still need internal volume to accomodate the helmholtz resonator, just not the port itself). The port is replaced by a passive cone. The only passive radiator subs i can think of off the top of my head would be offered by Salk Sound and Funkywaves. So perhaps try to get in touch with them. FW doesn't really have an offering like that but might be able to do it custom to your needs. I would ask about a small SDX-10 based sub with passive radiators. And of course Salk has their Salk Songsub, with bass down to 22hz.
I believe sunfire subs maye have an offering for you although i've never really been a believer in 8 inch or brick and mortar subs but you might want to hit up your local sunfire dealer and see what you think.
Another, more out-there alternative, would be to go infinite baffle. It can be a bit more inconspicuous in one sense, although in another sense you have holes in walls.
