That's interesting fhw.
I came across the same scenario as you although the opposite of your experience with my vp150.
My centre dialogue was originally too loud and i had to notch it down a couple of dB. But i haven't tried alot of movies yet, 2 to be exact since i got the vp150.
I'll let you know if any of my future movie rentals do the reverse. Variability in sound mixing between different movies certainly would explain things. I know for certain that some dvds come with DTS 5.1 coding while others don't.
I'll snap up some more dvds next week and see if i encounter your condition as well.
"Those who preach the myths of audio are ignorant of truth. Research begets reality."