I don't believe AA serves BCN to DTW without at least one connection. On which segments were you downgraded? Were you given the option to travel later in business class? Where you offered any special (exit row, more legroom, etc.) seats in coach or was the seat next to you blocked?

I suspect the answer is EC261, which specifies a refund of 75% of the price paid (not including tax, etc.) for the portion that was downgraded. The BA forum has a discussion of the regulations for award tickets and tickets upgraded with instruments.