Quote Originally Posted by Dread Pirate Robert
most AVRs stupidly low-pass filter the subwoofer pre-out at the crossover frequency, which means that you could lose some of the LFE signal from the crossover frequency to 80 Hz.
Note that I said "most AVRs"--some do this right, and if yours has independent crossover settings for each speaker or type of speaker, then it's a pretty safe bet that you can set your crossover lower than 80 Hz without missing out on any of the LFE signal.