REL seems to have a different philosophy than other sub companies. Other companies suggest using the line level input and setting the crossover the way you suggested. REL recommends the high level and setting the crossover really low, around 25Hz but setting the level fairly high. Their reason is that most speakers are really full range taking into account the room. I split the difference. For music I drank the REL cool ade and set the crossover somewhere in the 20's and the level fairly high. For HT, line level, crossover at about 45Hz,(my Sonus Fabers Concertos go down to about 40Hz). I would just experiment and find out what works best. Have some fun and find out what sounds best for you.