I guess everyone will have a different taste as to how much/little bass they have in any one source setting. My goal is to always get the most out of my left and right mains and have the subs compliment that effort.
Depending on what sub/subs I am using in my system, I find output levels vary...nontheless, I never really have to set the sub output past 1/3 value and pre out signal level from my receiver can vary from -5 to +2, depending on the source.
If I notice a specific source is heavy or light in the bass dept, I simply adjust the pre-out signal to make it sound good to me.