I've got the VP150, with M60 fronts, and QS8 surrounds. I think that it is a pretty solid system. Keep in mind that many people (myself included) have the ability to adjust speaker settings quite a bit at the receiver or pre-amp area. That could be a reason for any perceived tonal differences. As an extreme example, you could not use a sub, and pump everything to the R/L fronts with a "boost" in dB on the receiver, and then set the center channel to be less "boosted" in volume, and be set to "small" or some other obviously non-matching setting.
Then it would sound pretty bad in regards to a smooth sound field.
