Sub Questions: Speaker-level vs Line & Crossover

I've got a pair of NHT Classic Threes that I'm going to be pairing up with a newly acquired Velodyne Optimum-8.

This is a music-only system. Absolutely no movies, etc.

First, connections: I've got Audioquest Type-4 cables to the NHTs and I have a spare set on hand that I can use for the Velodyne. Is there any reason I shouldn't just do this in lieu of purchasing 10' interconnects to go from the pre-out on my amp to the sub? Just don't want to spend the money if there's no sonic benefit from it.

Second, crossover setting: I'm planning on running the Classic Threes at their full range - I'm very very happy with how they sound and just want to augment the lower registers with the sub. I, also, don't have a processor loop on my amp short of the tape monitor loop. At any rate - I want to run the NHTs fully.

That being said, where should I start experimenting with the crossover setting on the sub? The -3db point of the NHTs is 45hz. Both the NHTs and the Velodyne are sealed enclosures so, if I understand correctly, they should both roll off at -12db/octave, which should make integration easier, right?

Any input on either of these issues is greatly appreciated - thanks!