Wow! Great setup! There are not many board regulars who have M40's, and fewer who have tower speakers all around for surround. Please stick around and give us the benefit of your experience.
If it sounds tremendous to you, that's all that matters. Don't let the allegedly "expert" opinion of your friend compromise your enjoyment. Some people are predisposed to say that unless your speakers are not all identical, they can't be sonically matched, regardless of whether they can actually hear anything that supports the theory.
In what context did your friend make this observation (what kind of material and processing, etc.)?
There are some people who think that the M2/M22/M60/M80 sound a bit more forward than the M3/M40/M50. I do not have personal experience with the comparison.
Really, unless you honestly hear something that YOU don't like, I'd just smile and enjoy the music. Everybody's ears are different.
