Denjo,
Left and right are from the perspective of your listening position. Tapping the left and right channels of your preamp into the subwoofer means your capturing both channels bass, not a bad thing! The Force XL subwoofer has a fixed power cord, not sure about the older Force subs but upgrading power cords even on a sub is not a bad idea. I wish Mike would have done that on the new Force XL. Depending on the distance between the preamp and the sub will determine whether or not you should use a shielded interconnect. In this case leaning to the cautious side is not a bad idea. Sub's will benefit from a good interconnect just like the rest of the components in your system.
If your feeding your subwoofer from a processor using the .LFE output, a single connection to the sub is fine and you usually use the left input on the sub or the line in depending on your subs configuration. If you only have one cable to use and your using a regular preamp, people usually use the left channel output to go to the sub.
