How exactly does the crossover work on a receiver? I know that if it's set to 80hz then only those signals above 80hz will be sent to the satellites, but what about the sub? Are frequencies above 80hz not sent to the sub? Is there a 'grey area' around the crossover so that the sats and sub can blend? The reason I ask is that my sub (Acoustic Research HC6) has it's own adjustable crossover. If the receiver is not sending signals above 80hz (as an example), then why would the sub have an adjustable crossover to 150hz?