Yes male voices could play through the sub if you have the crossover set high enough for that to happen, will it sound "right?" Maybe yes maybe no, if the sub is crossed over perfectly, is positioned correctly and gain is set correctly you should never know the sub exists, the sound will be seamless and balanced. If your running a center channel and the sub is not hooked up to the center channel the chance of voices being transmitted throught the sub will be on the rare side. In my 3.1 setup, the sub is hooked up to mains, there is rarley dialogue from the mains, its all handeled by the center. The mains are transmitting music and effects with the occasional voice if its off center of the image. Contact me through email if you have more specific questions, i will try to help the best i can. If you hook up the speakon and LFE inputs and get a hum out of the REL i can tell you how to eliminate it, I dont beleive the REL manual describes waht to do when this happens.
As far as aftermarket speakon cables, i heard a differenece. Since your just getting the sub i would wait and get famialir with the sub, play with postioning it etc. RELs are easy to make sound "good" with little time setting them up, once you get familair with them and really start tweaking is when they really start sounding great. Take some time setting it up in the beginning, let it break in for a couple hundred hours then come back to it and dial it in.
As far as aftermarket speakon cables, i heard a differenece. Since your just getting the sub i would wait and get famialir with the sub, play with postioning it etc. RELs are easy to make sound "good" with little time setting them up, once you get familair with them and really start tweaking is when they really start sounding great. Take some time setting it up in the beginning, let it break in for a couple hundred hours then come back to it and dial it in.