It seems that a lot of people just hook off one speaker. Is it always the rule that base is equalized across the left and right channels, What happens if low freq signals are different on the left and right channels it would sound funny, right? as which ever channel is not going into the LOC is not going to get picked up by the sub. Is there anything wrong with running the extra wires from the other speaker, I assume that you want to use shielded cables to cut down on interference.
Another question, what size sub did you use I can't make up my mind between 10 and 12 inch. I don't do rap mainly Death Metal but I do like 80's and a lot of 70s stuff as well. I don't think I want to use a ported box I want punch over boom so I'm gonna go for fully sealed box for a tighter response. Fear Factory and Slipknot have insanely fast kick drums.