I saw it and thought the last thing I'd worry about being "wrong" was Athos' voice. The whole thing was such a mess that it detracted from even a single word that most of the cast said during any point of its' runtime.
I watched it two weeks ago and I've forgotten roughly 90% of the movie. This rarely happens for me, and in this movie's case I'm grateful.
That doesn't help you at all, but honestly I don't remember someone's voice sounding "synthesized". Among many other things I don't remember...