Elmulticine has an exclusive interview with Matthew Macfadyen in Spanish. You can read it in its original form HERE. (found by Carmen!)
Below is the slightly cleaned up Google Translation into English. Hopefully it is close to Matthew's actual words:
Interview with Matthew Macfadyen talking about The Three Musketeers and his projects
Matthew McFadyen is the versatile actor who plays the musketeer Athos in the new 3D version of "The Three Musketeers." Versatile because he has been very successful in the theater, in television ("The Pillars of the Earth") and also in film with movies like the celebrated adaptation of Jane Austen's novel "Pride and Prejudice" with Kiera Knightley and directed by Joe Wright, with whom he will work again in his next project. Has given rise to a multitude of classic literature and, on the occasion of the presentation of "The 3 Musketeers 3D" at the Festival of San Sebastian, we had the opportunity to conduct this interview.
September 30, 2011 / Javier Tamarit Lacomba
Elmulticine.com: What are the differences between the interpreter and Athos shown in the previous movies and the novel?
Matthew McFadyen: I do not know, I do not know the previous versions. Athos, I've played as I have found in the script.