I had both the M80's and the VP150 and I thought they were timber matched fairly well but not perfectly. Average for lack of a better word. I can't however say that I thought the difference was as pronounced as you are describing but it was there. Are both tweeters working in the VP150?
I personally have never thought they should be different. They don't have to be timber matched as these day's that is almost a buzz word but they should be darn close.
My current set-up sweeps left to center to right with very little if any noticeable tonal change in the highs. I would hope that given the interaction between the mains and the center this would be the norm.
