I think there are 3 subwoofer connection strategies:
1) RCA from pre-amp to subwoofer
2) Hi-level speaker output from power amp to hi-level inputs on subwoofer; and then connect subwoofer outputs to speakers.
3) A strategy recommended by Blumenstein audio: hi-level speaker outputs from power amp to speakers, and then piggyback from the speakers to the hi-level speaker inputs on the subwoofer(s).

I think the third option argues that this approach allows the main speakers to get all the "benefit" from the power amp without possible adulteration from the subwoofer crossover.  With the understanding that my decware set amp is very revealing, I think I lean toward this 3rd option.  It sounds good to me anyway, but I'm wondering what this forum knows about this.  Any thoughts?  It would be neat to see what Steve D. thinks.

TomFrei- I would agree with Donnie about # 3 being the best option (imho). When I set up our listening room for the Decware/Omega system, the speaker wire I pulled is an AQ four conductor cable, so I have all four conductors connected at our Rachael (per channel) and then one pair to the left speaker and the other pair to the left high level input on the subwoofer and then same for the right channel. Amp straight to speaker and straight to sub. I did play with the stereo RCA out of the Rachael to the RCA in on the sub, but felt the high level was best. Let us know how it pans out for you and happy listening, Chris.

I like 4) as mentioned by hdrider; speaker wire from main amp to speakers and speaker wire from main amp to sub amp.

No, but you can run different wire.