I'd try your itinerary on the Booking Tool as I was looking at EF for availability today for AMM-BRU and AMM-MAD and even though EF was showing lots of D0s the tool was able to book the flights in D.
I don't know what the issue with IB is but to confirm what Gardyloo mentioned when trying to commence with a CAI-MAD flight the tool did not give the option of the direct IB flight.
The other benefit of taking RJ ex-AMM is that the tool books through AA which might help lower the fuel surcharges and I have found changing reservations much easier with AA issued tickets - you don't have to pay Service fees for every date change.