Rick, they don't do the same thing: the crossover in an HT receiver is a real crossover that rolls-off the sub above the selected frequency and also rolls-off the speakers below that frequency; the "crossover" control on the sub itself is simply a variable low-pass filter that affects only the sub. The speakers aren't affected at all by the control on the sub and continue to play whatever their full range is, and this is the case even when the main speakers are connected through speaker-level outputs on subs that have them.
So, the suggested settings for the EP500/600 "crossover" attempt to roll-off the sub above where the "natural" rolloff of the speakers begins. This might achieve a fairly good blend, but the bass management on the receiver does it more precisely and also takes some of the low bass load off of the speakers. When available, the receiver bass management should be used.
