I've never been able to keep any other cichlid with regani in my 150 gal. I had to rescue a dovii because the regani had it pinned in a corner.
Although it hid any time I entered the room, eventually it killed its mate, I gave it to a friend with a larger tank, and it killed his red devil and carpintus, both larger than the regani.
My guess would be a school of swordtails or Astyanax tetras might work.