Best Big Sub? or duals?

I am not concerned with music as much with HT. I am running vandersteen 5a with two 12" built in subs in the main speakers. They are increable and rock the room for music. I need more something for effects and i do listen to some dts music dvd's so it can't be all movies. But I want to feel explosions in movies.

I would look at REL. I have a Stentor and couldn't be happier.

REL is very good. I have just what you need for HT. A pair of Nelson Reed 1204s. They were designed by a California company for the movie industry to play back soundtracks at full volume in large spaces. They will reproduce 20 Hz at 120db levels. They use 4 12" Volt drivers on each channel, 2 forward facing and two facing back. The cabinets are large but not huge. I have the electronic crossover for them. When I used them on the cannons in the 1812 it would scare you. They were only used for a year or two before I moved into a smaller house and packed them up , where they have been the last 14 years. They were reviewed in Stereophile in the late 80s. I will sell them for$2900 with crossover, which is a fraction of the cost of building something like this now. The freight will be considerable , as they weigh 110lb each. I had intended to keep them but my present listening room will not hold them and I do not contemplate moving. There is info on them on line.

JL Audio Fathom F113 or 112

Parts-Express has the Titanic subs and a few of them use the Dayton Reference drivers.These probably aren't necessary ,due to being used strictly for HT.I use 2 subs,each with two of the Reference 10" and the IB woofers for LFE.They have on sale the D-dub kit for $320.These have 15" woofers mated to 240W plate amps.The Titanics are about $750 each,though they do have 1000W and a parametric EQ.