Around 100 Hz is when bass starts getting more directional. If you set your crossover that high, it can interfere with the imaging and sound stage of your mains. I'd lean toward crossing over @ 80, but ultimately you should trust your ears. If the placement of your towers puts their low range in a room null, then a 100Hz crossover point for your LFE channel might sound better.
One of these days you ought to graduate from those toy subs and save up for something that'll dip down into infrasonics (below 20Hz). That NXG that afterlife2 linked would be a nice step up; or if you could save up about $600, a plethora of options for more grown-up subs opens up for sound you didn't think was possible. Although I'm not surprised that you prefer the Cerwin Vega sub over your Onkyos, I suspect you're still missing half the LFE experience in your movies.
Heya afterlife2! Thought I'd stop by and see what's going on. Did this place fall apart without me?
