Go for the DD, it has parametric EQ. Given the 1.6 as I've heard it go down to about 40Hz, you might want to have a lower than 45hz cutoff for the sub.

I believe I talked to a Velodyne rep here in England at an audio show and he recommended line level rather than speaker level. To be honest, I doubt there's any difference between the two. But if you use line level for the sub and are not using an int amp for your 2 main channels, you'll need either two pre amp outputs on your pre amp or a a couple y splitters to be able to connect the sub.