Interesting link. Yesterday, I finished hanging the plasma on the wall (pics soon). The change from a tube to the plasma meant that the center speaker (VP100, only) was moved from above the TV (~4.5 feet up) to around two feet off the ground, resting nicely at about the same level as the mid-range driver in the M60s. This placement was not only necessary, but prefereable from a cosmetic point of view.
I found the sound stage to be much tighter and panning was better. With the speaker lower, it is more at ear level, and voices are clearer and richer.
Comparing the two choices, I agree all the way with the problems associated with having a center channel too far above the other front speakers.
Now, of course, I'm itching to upgrade to a VP150 ... stop it, stop...[/swatting hand reaching for check-book]
