Han,
After almost a year of tweaking, I've settled on a 40Hz cross-over in my Denon and 600 for movies and most music. While this leaves a 35Hz gap in my surrounds, I haven't found it to be a problem. I enjoy the "tight" sound of the 600 when it is crossed over this way.
I've found that this setting works for all movies in my environment but not necessarily music. I find I have to very often tweak the cross-over settings depending on the music I'm listening to.
Regardless of the setting, the 600 blends in beautifully with all speakers.