If you have stereo inputs and outputs on the sub, then do what I do. Simply run your main output to the sub input, then run the sub output to your main amp input. This will give you extra dynamic range.
Pre amp to sub hookup, or speaker level?
If my pre only has one set of main outputs, how do you recommend hooking up a subwoofer? Is it better to use a Y adapter and split the signal out of the pre, or run a second set of speaker wires from the amp? Is it ok to run a second set of speaker wires off my 2 channel amp, or does that interfere with its main speaker driving duties? Thank you