i found that the best way to search was to put all the sectors int the advance routing fields, specifying airline=AA. this then makes it easier to delete an airport code and replace with another. eg I found that LAS was causing me trouble and replaced with SAN which fixed the outbound farecode (I think the fare needs I availability and, for some reason, N econ availability - but I might be very wrong on that!)
I had to use different routing on the way back to get the fare code back to the cheaper one. I also had to move STOPS to be No Limit.
Search was something like this (not sure I needed the AA at the front of the routing list)
I eventually booked this run, which was about £899 when I booked it (via Powertools, AA.com) :
