Subwoofer Selection HELP ? ? ?

I am re-building my system for a media room. I have all Magnepan speakers (3.6, and all MMG-W's for center, surrounds), with Bel Canto Ref1000 and Parasound A52 run by a Cary Audio Cinema 11. I really am struggling with what sub to get? I have not yet, but plan to buy a turntable and I have a Denon 5910 (being modded), so I love to listen to 2 channel music, but the room has a new projector and will definitely be used daily for movies/video.

All that said, I want one big sub. I have narrowed my choices to;

Definitive Techology Trinity

JL Audio Fathom 113

Revel b15a

Velodyne DD-18

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I think the trouble may be to get that fast bass for music may not be ideal for the lowest blast and booms for movies but I would say a sealed sub design is just about a must.
If you want to save a bundle, go a little vintage, and don't mind a large clunker size cabinet, I used (and still do) a Velodyne ULD-15 series II with my original MG IIIa and later my MG 3.6Rs with great success. It would be hard to beat for Movies and was suprisingly fast in mating with my MGIIIs and MG 3.6Rs.
I'll second the SVS rec. I've had a PC13 Ultra (cylinder version) for a couple months and it is a beast for movies and quite musical as well for half the price of the Fathom.

It is "fast" enough to keep up with my Martin Logans effortlessly.

I consider it steal at $1500 (shipping included).
Nice subs no doubt. If I were to choose from your choices it would be Velodyne DD-18 then the JL Audio Fathom based from years being a Velo dealer. The JL Audio could easily be my first choice though as well. That's a tough call.

Another sub we are having great success with is from Triad speakers. Specifically, the Triad Gold/Platinum PowerSubs. Both are as good imho as the others mentioned and are less expensive. Plus, these are righ-sized unlike some of the ID brands that go for shear output and are as big as Volkswagons in your living room. Ouch!
I had stopped thinking about the SVS, but what about a PC Ultra Cylinder and one of the smaller box subs for music? I wonder how that would work? Maybe a perfect marriage???

OK, I have just made an executive decision and bought an SVS PC-Ultra 13 online. If I like it, I may buy a smaller version for music, or....... watch this website in the coming months for great deal on a big booming sub!!!
Have you thought of going the infinite baffle route? Google "Cult of the Infinitely Baffled" and check them out. If you are looking at bang for the buck these are it.
Although it's not infinite, budget was not the big consideration. I had budgeted about $3k for a Sub/Subs, I really want the performance for both music and movies. I will spend more if I need to, but why if I don't? I am looking forward to seeing how the SVS does now. If it's not satifactory for music, I may add a JL Audio Fathom 12 or Velodyne DD-12 and go with 2, which I wanted to avoid, but maybe it's unavoidable.
You won't be disappointed with the PC Ultra.

If your Denon "remembers" bass mgmt settings for different inputs you're all set. Haasle free for movies and music.
I've never heard a sub as tight as the RELs, britannia series
Sorry to muddy the waters... but I'd be looking at the REL Stadium or Aerial SW-12.
OK, I got the SVS, this thing is a massive beast. My front Maggies are in beautiful Bear Lake, MN being fixed, so I have not tried to integrate it with them yet. But I did plug it in, and hook it up and play some movies, just to try the LFE effects. Wow, this thing can move some air.

I think I am going to cheat and buy a Velodyne SMS-1 to integrate it. Anyone have any experience with the SMS?
I think you went the best route. SVS makes amazing subs. Ive owned paradigm servo 15 (stereophile a / b) the hgs 18 velodyne, the martin logan descent, and none of them sounded as good on music or movies as the svs ultra/2. I will say a sms-1 takes it to another level, I bought one and love the combo. Why pay more for subs that really dont give you any more. Im convinced most people just think svs isnt as good as the others mentioned because of its price. This goes to show paying more doesnt always get you more.

note**I must admitt I only run my sub at 35hz crossover point because of my large full range focus 20/20. Maybe it wouldnt do as good for bookshelf speakers for music. I do stress MAYBE.