hi joe - im sort of like you, i have a large tank with 4 silver dollars - however, i do believe you can mix cichlids - as i have to be honest, heres a vid - they all live in a well balanced tank - treated like gods, fed like queens.
http/www.youtube.com/watch?v=DLGa8d9L1SY...re=channel_page
http/www.youtube.com/watch?v=DLGa8d9L1SY...re=channel_page