For music only go with OB all the way. You'll have a hard time wiping the grin off your face 
Just beware of the monster you will be creating. Look at Jay (Captainhemo), he started off with one dual 12" driver OB sub and now he has two triple 12" driver OB subs, one for each channel Bwaaahhhaahahahahaha !!!!! 
FIY, if you go with the SW-12-16FR drivers you give up some output over the 08FR's but if you decide you would like the three driver version later on you would only have to buy one more driver. The A370PEQ amp can drive two of the 8 Ohm or 3 of the 16 Ohm drivers.
Mike
Don't use me as an example of the "monster he's about to release", give that honour to Rich (HAL)
http://www.audiocircle.com/index.php?topic=140374.0 
Mike is right, for music , you won't find better, the detail and accuracy of bass is amazing.
Regarding the SW12 08FR / SW12 16FR, yeah, you do sacrifice a bit of maximum output by using the 16's , but een when I had a single dual H-frame with 2 SW12 16FR's, I did not have to max out the gain to reach sufficent SPL levels in my roomn. If you are interested in the 16 ohm version to keep an upgrade path open, you'll need to talk to Danny about shipping dates.
Interestingly enough, as I've upgraded the subs, first from the single dual h-frame to 2 dual h-frames, now to dual triples, it is not about the SPL (for me anyway)... it is all about the extra weight , or impact, you get by moving more air. Even at low volumes, the larger arrays just seem to creat such a foundation . Seems the more drivers used, the more ambiance you have. That being said, until you hear more, you won't find anything lacking with the duals, I'd have never gone to the triples if I hadn't built a set of triples for Don and tested them in my room (big mistake

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I know you had a similar feeling Mike when you switched from the 8's to the 12's ... I can only imagine how Rich's and Steve's dual 6x12 towers sound

Another way to go is to build one dual-12 OB sub for now, and enjoy it while you save for a second
+1 That's my plan. Anyone in Austin interested in my 15" sonosub?
That's how I started Hank, it actually worked quite well too

I've paired the pair of dual 12's with OB7's, NX-Otica's, X LS Encores, PMC TB2 Signature's and Piega P10's, they were extremely easy to integrate with each. They truely bring the performcance of each to incredible levels. When my buddy brought the PMC monitors over, he was blown away at the difference the subs made and by how simple they were to dial in.
jay