Originally Posted by
GRU787
Can you use the Mileage Multiplier sold by AA on top of all miles earned on this promotion? Does anyone have done that?
Sure - I don't see why not.

The Mileage Multiplier is calculated on the "base miles" of your itinerary. Your elite bonus miles, separate promo bonus miles, etc all have no bearing on the Mileage Multiplier program.
Edit to add: By the way - Welcome to FlyerTalk and the AA Forum,
GRU787!

(I just noticed that you were a new member. ^)