Setting Sub Crossover Freq

Thanks all for your input. I the case of polarity...I'm having trouble. Is there a precice way to know, other than by lisening for "more bass" ?

Mjmch, are you running through a high-pass crossover to main speakers and a low-pass crossover to sub, or are you instead letting the main speakers run full range and connecting the sub via line-level or speaker-level inputs from preamp or amp? These are two very different approaches. If taking the latter approach, you are only adjusting HF roll-off of sub, and would therefore want to do so at a frequency at or beneath the useful bass output of your mains.

Dgaarretson, I am running RCA outs from my pre into the RCA inputs on the Sub. (I'm running balanced from the other pre outs to my amp, which is then powering my speakers--full range).

This is an excellent way to go unless one has a high-quality full-function outboard crossover to perform high-pass hand-off to main speakers. Mediocre electronics of high-pass crossovers typically found inside sub cabinet are likely to degrade sound and cause more problems than are solved. You might first try the low 40hz point with a sharp 24db/octave roll-off. After you have experienced how clean things sound up into the mid-bass and mid-range, experiment with more gradual roll-off and higher crossover points for comparison. I bet you will find roll-off at higher frequencies is muddy.