in a large enough tank you could keep some more peaceful cichlids like severums with a trimac, but when I say large enough I mean crazy large...like 8' L x 3' W or bigger. however....rams? come on...we do have to exercise a little caution. no matter how big the tank, keeping a fish that will be no more than bite sized as an adult is never going to be a good idea. 
with the bigger, more aggressive cichlids it's always trial and error. I've seen several member's who've kept fish like trimacs, fh's, rd's etc with clown loaches, silver dollars etc with no issue. but that doesn't mean it'll work for everyone.
the best thing you can do is try out a combination, but have a backup tank that someone can be moved to should things go south.
with the bigger, more aggressive cichlids it's always trial and error. I've seen several member's who've kept fish like trimacs, fh's, rd's etc with clown loaches, silver dollars etc with no issue. but that doesn't mean it'll work for everyone.
the best thing you can do is try out a combination, but have a backup tank that someone can be moved to should things go south.