A full grown oscar is too large for 90 gal tank.
I wouldn't get anything that maxes out beyond 9".
What are your tap water parameters? Hard? soft? High pH, low pH?
To me, these parameters will help determine success and health of the type cichlid added.
I try to match the fish I keep, with the water parameters I'm dealt.
For instance my water has a pH of 8.2, and mineral rich.
To me it would be ridiculous for me to choose a soft water species like Uaru, severum or a soft water Geophagine that live in pH 5 (or lower than 7).
You may also consider that some cichlids do well alone as a single specimen, some do best in shoals (if your tank is large enough)
Thorichthys and Cribroheros are shoalers, and when kept as a lone cichlid specimen can become hyper dominant, and attack anything that moves in the tank.
Any Vieja I've kept get too large for a 90, and "can" also get hyper dominent if other fish in a tank the tank they're in doesn't have a length of at least 6 ft to exercise in.
Some of the genus Nosferatu might work if your water is hard and mineral rich, and there are "no" other cichlids in the tank, and they probably will ignore the Senegal.
Most remain the right size, and are loners.
Here are a few.
Nosferatu bartoni .
Nosteratu pantostictus
Nosferatu pame
