I know a lot of you have this configuration. I was using my Behringer B212D's prior to the K12's. I would run the B212D's thru the mains and the KSUB thru AUX6. There is one reason I do that. No matter what type of crossover you have, running the mains thru the KSUB and to the K12 or B212 as tops, you still end up with some frequencies that don't need to be in the sub at all. If I run the sub thru AUX6, I have full control over what instruments I want in the sub at all. I'm open for ideas if anyone can convince me otherwise.