I own a DD18+, but my system is solely for music. I'm impressed with the DD18+, it has remarkable output, and even in my very large space a single DD18+ is startling on organ, special effects, and synthesizers than get below 40Hz. The new DD Plus series is an entirely different animal than your previous generation DD15.
I auditioned the JL 212 twice. For home theater use the 212 might be a little better. I think it has more absolute output below 30Hz than the DD18+, but I don't have measurements to prove it. They sound "big". The 212 was actually my first choice when I was shopping, but I never heard it blend in for music as well as the Velodyne did, so I got a Velodyne. (I actually auditioned a DD15+, but the DD18+ is nearly identical with more output.) Also, the high-pass filter on the DD18+ saved me the expense of a crossover like the Bryston or a new digital pre-amp with bass management (like a Classe), and that's not a consideration for you with a D2v.
Nonetheless, I can't imagine you'd be dissatisfied with either choice.
I auditioned the JL 212 twice. For home theater use the 212 might be a little better. I think it has more absolute output below 30Hz than the DD18+, but I don't have measurements to prove it. They sound "big". The 212 was actually my first choice when I was shopping, but I never heard it blend in for music as well as the Velodyne did, so I got a Velodyne. (I actually auditioned a DD15+, but the DD18+ is nearly identical with more output.) Also, the high-pass filter on the DD18+ saved me the expense of a crossover like the Bryston or a new digital pre-amp with bass management (like a Classe), and that's not a consideration for you with a D2v.
Nonetheless, I can't imagine you'd be dissatisfied with either choice.