There are a couple of very likely possibilities here:
1) It sounds as though you have a very large volume of space that you're trying to pressurize. The sub doesn't "know" where your listening room ends and your kitchen begins. It doesn't "adjust" for an open ceiling or a sloped roof. So far as the sub is concerned, it is trying to pressurize the entire open space, and it sounds entirely likely that the 400 Watt 12" PC-12NSD simply doesn't have enough output to pressurize your entire open space. And to be honest, from the sounds of it, I think you might have been expecting a bit too much. I'm not saying you're wrong at all to have expected a lot. SVSound's subs are extremely impressive - especially at the price - but they are not magic. They can't overcome physics. People ooh and ahh about them and deservedly give them praise, but most people also have a much smaller volume of space that they are trying to fill.
So it's about managing expectations. I can totally understand how you were expecting more based on what you might have read. But it is also too much to expect a 400 Watt 12" subwoofer to fill a huge volume of space with high SPL bass.
2) It's also entirely possible that you are simply sitting in a bass null at the particular frequency where you are expecting to really get hit in the chest based on what you've heard in your car. You say that you've tried several positions, so this might not be the reason for your disappointment. But at the same time, it is only certain, specific frequencies that will form a standing wave with nulls and very large peaks. If you happen to be sitting in the null of that particular frequency, no amount of additional output is going to solve that problem! The only solution is to move (either the sub or your seat) out of the null, or to use a second subwoofer to create more even frequency response throughout your room at multiple seating locations.
I would recommend before you lose all hope and before you declare the PC12-NSD to be a failure for your usage that you try "crawling for bass".
Put the subwoofer in the spot where you normally sit (push your seat out of the way first, obviously
). Now play a repeating bass sweep. I like to recommend using a THX DVD or Blu-ray and using the last Audio test in the THX Optimizer, which is a sweep from 200Hz down to 20Hz. Just put that chapter on repeat so that the sweep plays over and over continuously.
Now crouch down so that you are at seated height. In this crouched position, go and listen in the spots where you are reasonably able to put the subwoofer. Try moving around a little bit - even just a few inches can make a difference. Listen for a spot where the entire THX bass sweep sounds smooth and even in loudness all the way from the top to the bottom. With just one subwoofer, this might not be possible, but try to find the spot where the majority of the sweep is evenly loud from top to bottom. Mark that spot, put your subwoofer there and then push your seat back into position and have a listen. With your positions reversed, you should hear the same even, smooth sweep at your seat now!
3) You might also want to try decoupling your subwoofer. In most cases, people find that the bass actually seems a bit quieter when they decouple their subwoofer because they are used to the subwoofer physically shaking the floor, which adds noise and distortion to the room, but makes the bass seem louder - even though it's less accurate and full of noise. But in some cases, the physical shaking of the room adds enough distortion at just the right (or wrong, depending on how you look at it) frequencies to interfere with the bass coming from the sub and works to cancel out some of the bass energy, much like the null of a standing wave. Decoupling greatly decreases the physical shaking of the room due to the movement of the sub when it is placed directly on the floor. By eliminating the physical shaking, you get "tighter", cleaner, more accurate bass that has less distortion. Like I say, this might actually make it seem quieter. But yours might also be a case where the added distortion is making things seem quieter, in which case, decoupling will help. I recommend the Auralex SubDude for SVSound's PC cylinder subs. The feet of the cylinder subs fit perfectly onto the corners of the 15" square SubDude
Again, to be completely honest, I think this is a case of simply having too large a space to fill for the capabilities of the sub. But try the other potential solutions first because they cost very little or nothing (except time), so why not, right?
If you discover that the PC12-NSD simply cannot produce enough output for your liking, then it's time to get another sub. You could simply add a second PC12-NSD, but you would need to co-locate them (ie. put them directly side-by-side) in order to really gain anything in the way of increased output. If the PC12-Plus costs too much, you might want to consider one of the HP (High Output) subs from Rythmik. The FV15HP in particular offers very similar output and performance to the SVSound PC12-Plus at a lower price.
To be blunt, if it were me, I'd want a pair of PC13-Ultra subs in a room that size, but obviously, the price for that goes WAY up from your $800 mark. The simple fact is that you might not be able to achieve the sort of output that you are looking for within your budget. Sadly, there's no magic. When you've got a large volume of air, it takes a ton of energy and surface area to make it move! I'm sorry that the PC12-NSD wasn't up to your expectations, but I hope that you'll be able to get past the emotional disappointment and realize that having limitations doesn't mean that the product or the brand are crap. It's just a matter of physics. And you wouldn't blame a Honda Civic's engine for not having the power to make an M1 tank go 100 mph
