How about a female carpinitis for your male? It would be easy enough to do as m/f are distinguishable by the black patch in the dorsal for females. You could also look into other female fish if you felt like playing around with hybrid spawns - not exactly my thing, but would be a change of pace if youre getting bored.
I don't like more than one aggressive cichlid in a 4footer - never ends pretty. I've found lyonsi to be fairly slow & smaller growing than most other amphs & not as aggressive overall. You could get away with a pair in a 75 for a good while (w/o the carp of course) before they would eventually need more room. Great looking carp btw!