How to audition subwoofer?

Would any please tell me how to audition a good subwoofer w/o dragging my own subwoofer to the store? I have a Polk Audio PS350 (10" 150w w/ variable crossover 60-160Hz & frequency response from 25-180Hz). I went to the Good Guys to audition a $1200 Velodyne sub (sorry don't remember the model #). The rep closed all the doors of the sound room, put in the CD, and cranked up the volume of Parasound separate system. It sounded so boomy that I didn't find it any better than my current sub even though two salemen used the exact same lines, "Velodyne would blow your sub out of the water." I was thinking how? By shaking my room? My 12X13 room was already shaking with my current sub. I was hoping to hear the tight bass that I have heard from this websites and others similar. They told me to bring my sub in for side by side testing, but before I do so, I like to consult with Audiogon members, i.e. how do you audition a thousand-dollar subwoofer. What is the trick? My preference is 1:1 of movies:music. Do you prefer dual 12" for push and pull? Do you like the down firing? If I get a better sub, I was thinking of stacking them and use a Y splitting cable. Or should I just forget about upgrading to a better subwoofer by taking an easy route, i.e. getting another PSW350 to place each behind a main speaker to get better marginal affect. Any personal experience. Please shed lights. Thank you for reading.
I like the idea of putting a SW behind each main speaker. I think this provides the best "seamless" integration. In particular I have my Maggies set up this way with dual driver subwoofer systems installed in the wall behind each of three Maggies. The idea is that they "play through" the screens, and it seems to work. The thought has occured to me that the function of the SW may be as much to absorb the out-of-phase backwave of the planar speakers, as to directly generate LF sound.

When auditioning a SW, remember that most LF sound sources are not exactly crisp, and a somewhat lumbering (not "tight")sound may be correct. It takes a while for a 30 foot organ pipe to get itself going, and the same for other LF instruments. Compare a tuba with a picalo. Percussive bass, like a drum is the only exception I can think of.

I think the Velodyne is good, but the cost of three could not be justified.
Find several pieces of music emphasizing different kinds of deep bass. Classical (i.e. Antartica suite on Naxos), upbeat & funky (i.e. Marcus Johnson Chocolate City Groovin), acoustic upright, big drums.

Then listen to speakers similar to yours both with and without the sub turned on. A good sub will be able to handle both the rumble and the punch, while adding the dynamic and enhancing the bloom higher in the frequency range. The salesman should allow you to adjust the sub, if necessary.

Basically you shouldn't notice that the sub is there, except for the qualities I mentioned above. If the room is overloading it's set incorrectly.

My personal preference, although a tad expensive, is the REL Strata III. Integrates with most any speaker & gives you what I describe above.

For music, I think a sub works best with the output (volume) set very low, so that it just fills in the bottom octaves without overwhelming the music (or the room). Forget the room shaking demonstrations, unless you're really concerned with movies.

One of the things I do when comparing subs, is to put my ear on the cabinet. How does it sound? Clean? Muddy? any rattles in the cabinet?
Bob hit the nail on the head. IF you notice that the low frequencies are obviously coming from the sub then the sub is not integrated. It's that simple. If the salesman can't make this happen then I would not buy a sub from them. I also agree with his recommendation of a REL strata (I own one, and I really can't tell that it's producing the bass until I switch it off). You can get a used REL strata for under $900.
Salesmen who sell subs according to power rating or ability to knock pictures off the wall are selling for home theater, not music.