Perils of the Writer: Rooms Full of Echoes

I've talked several times in the past that my real gateway into "traditional" fantasy was David Eddings.  One of the complaints laid against him, which is a pretty fair complaint, is that all his characters talk with the same voice, have the same sense of humor.  Certainly this phenomenon increases as you go later in his career.  Books like Regina's Song or The Redemption of Althalus have a core group of six or so characters who are all, more or less, the same person talking to themselves.
How do you avoid falling into this trap?  How do you give each character a distinctive voice?
Part of how I deal with that is going back to my playwriting and acting roots.  Every character in the scene is going to have a different motivation, a different interpretation of what was going on.  I had to approach writing each character as if a different actor was going to tackle each one.
Now, I'm never one for selecting a specific actor for a character.  Well, that's not entirely true.  Part of my early process involves coming through headshots to find faces that match the one in my head, give myself a reference.  Never a "famous" actor.  I wouldn't want to let that infiltrate my process.
Keeping those things in mind keeps the interplay between the characters from being just an echo chamber of my voice bouncing around the room.
How about you?  How do you keep your voices distinctive?