Subwoofer Decision


I have narrowed my search to two choices though I am sure I will get comments steering me away from these.
Contrast Rythmik Audio 12G with Vandersteen 2Wq. I would like to get only one though I know a pair are best choice. Could maybe afford 2 Rythmik, but only 1 Vandersteen for now. The subwoofer would support Dali Helicons (4 ohms) biwired and driven by 2 mono McIntosh MC 252's at 500 watts each into 4 ohms. Living room size aprox. 24'x16'x8' placement not centered on 16' wall due to furniture (wife) constraints must stay put. Subwoofer placement needs also to stay there as well, I know this limits possible best choice for placement, my bad. There is room behind, next to, and between speakers. Any help help is appreciated.
128x128lowfreqguy
Best bass driver ever made is the Danley/Eminence designed and built by Eminence LAB12. It's in use by all IMAX and OMNIMAX theaters. Get any subwoofer using a LAB12 and you're set.

One example would be the BK Electronics Monolith Plus. Which also uses a 500 watt MOSFET amplifier. BK used to be the OEM manufacturer for REL. They were responsible for the ST range (Strata, Storm, Stentor, Stadium), which made REL famous worldwide. REL makes Chinese crap now. 

BK has my vote as the ultimate internet direct subwoofer manufacturer. If I had to choose another company, it would be HSU.

As for Vandersteen versus Rythmik, Vandersteen destroys it in every possible way. 
I have a pair of Hsu subs for my office. They are good, but not as good as my Vandersteen 2w's. 
B
I saw "Dunkirk" at an Imax theater when it first came out and the empty seat next to me rattled (amusingly) with the strangely staged bass under the seats…I've always thought Imax visuals are amazing, and Imax sound shamefully bad. 

I saw one sub designer’s quip: "A fast woofer is a tweeter". Fast in regards to a woofer is not used literally, but to it’s perceived lack of boom. Many factors contribute to boom, mostly the room. But Arnie Nudell didn’t employ servo-feedback woofers in his IRS, RS-1b, and other speakers for marketing reasons, and neither does Brian Ding in his Rythmik subs. Nor does Richard Vandersteen employ feed-forward in his for no good reason.

If you want to see the woofer that hardcore home theater DIY’ers have for years put in their subs, check out the TC Sounds LMS Ultra 5400 18" woofer. When last available (from Parts Express) it was $900-$1000 for just the driver. Insane motor (magnet structure), extremely high excursion (2"!) and SPL capability.

@wolf_garcia Dunkirk sucked. And what does an empty rattling seat have to do with IMAX subwoofers?