Turning the crossover all the way up on sub also assures "double dipping" when mains are running full frequency. Now, you can eliminate "double dipping" by setting sub to crossover at a point that mains are not able to produce low frequency, or you could set sub at highest crossover point and then set other speakers to small. These extreme means to get a result will not get a smooth result however because either the sub or mains/center/surrounds or operating at their limits. At any rate, in my system my mains can get down to about 40Hz and right now they're set to small to filter below 60 Hz, while my sub is set to filter above 60 Hz. I run all other speakers set to small to filter below 60 Hz too. I once had the surrounds and center filtering below 80 Hz but then the 80 to 60 Hz frequencies were essentially lost from those channels. Now there's no double dipping and mains/center/surrounds do not extend themselves to push into low bass arena. This scheme is accomplished via my OPPO 205 multi-channel bass management capability.