read the last few posts of this thread for more info on phase interaction (although i could write many pages on the subject! ;) ):

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=10&topic_id=5197&mesg_id=5197&page=

the feature you have on your deck is equivilant to a phase modifier (assuming it works on timing and not amplitude). it might be a valuable asset for tuning purposes, so you might want to experiment around with it for a little while if you happen to have the speakers hooked up to the deck right now. the info you gain from such an experience might help you make decisions rearding mechanical phase later on.