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.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated