My statement came from researching the Audyssey thread. Chris (from Audyssey) along with Mr Holman (creator of THX), have often stated that there is NO crossover of a sub, this really is a Low Pass Filter. Why would you be crossing over the sub? If you think about it, you adjust the crossover knob on subs to either bypass or to the highest setting, usually 120hz.
The THX recommendation of 80hz, is for the other speakers to crossover to the sub channel, not the .x channel. He explains that this should be set to 120hz, as there is no LFE above that point. For whatever reason, some manufacturers have started to include this setting.
Dave, not sure, but I would image if you set it lower, maybe your restricting the Low Pass Filter from receiving frequencies above the 80hz point. They would be in the twilight zone.
