LFE Content between 80-120hz

We really need more information to answer that. For example, what is the slope of the rolloff for the sub, what is the low frequency extension the main speakers you are using, and what is the rolloff for the main speakers. Subject to that information however, unless you are using a tiny little pair of bookshelfs, cutting the sub off at 80hz is probably fine. In fact, it may even be too high. Generally speaking, 80-160hz is the octave considered to be "upper bass". Any speaker beyond little computer speakers should be producing something in that region. The sub should be operating below that.

It's a 24db slope set by the equalizer. It's a piega subwoofer, and I don't know if it has its own internal slope. The main speakers have a high pass filter of 80hz. How do I know the slope of my main speakers? They are also piega.

I agree with Mark, 80 hz is plenty high for most systems, unless you have a problem I wouldn't try to go higher.

I am not familiar with your speakers. However, if the main speakers and sub are both by the same manufacturer, they are probably made to integrate fairly well with each other.

A 24 db slope is pretty sharp, so if the main speaker doesn't go to where the sub ends, you will get a bass suckout at the crossover point if it also has a sharp rolloff. Not so bad though if the rolloff is more gradual fro the main speakers. It sounds like you're okay.

The rolloff of the main speakers, if not stated in the speaker specs, would also be indicated by the crossover's specs. For example, a "first order" crossover will rolloff at 6 db, a "second order" crossover will rolloff at 12db, a "third order" at 18db, etc. If your speaker spec tells you the "order" of the crossover, you will know the slope.

I still think 80hz is pretty high for a sub unless you have really small mains. You'll know if it's too high because the bass will sound a bit too pronounced and it may even make your main speakers sound sluggish or slow.