My take on this...if you are able to localize the sub with a x-over of 60hz, your levels need to be matched. Your sub is probably playing too loud for the mains, and that is why they don't blend.
My opinion is that in a real world room (one with compromises to looks and the building around it) the sub will always be somewhat locatable. I am still playing with my sub settings to make it disappear completely, but when I am watching a movie I never notice it. I only notice that the sub is behind me when listening critically to music. But, I am running a x-over of 80hz (THX recommended) and also run the sub 3db hot because I like the tactile feel during movies.
