Cichla will be cichla. There will always be a dominant one. Its just how it is. HOw big is your tank and what is the decor like? I would do a wc and rearrange it up a little bit....add a plant or 2....maybe some new driftwood. And better yet some dither fish that wont fit in his mouth.
with cichla dithers would be oscars, severums other fish that will get bigger but arent super aggressive orinos by nature are jerks but when they find balance they are amazing.
breaking up tanks in thirds is the way i allways go if the first spot dosnt work the second one for backup usually does the job but theres always a chance so the third is there for a rescue .
i would recommend dithers for a solution if you pull the orino its still got an attitude when he gets back in the tank but you could pull him and then rearrange your tank add a couple dithers and then reintroduce him the more confusion the better .
Signs of dominance for him, weakness for them. My managuense were the same way fighting but one did not back down from the other. I guess they eventually both said if you can't beat him then join him and now they have been together for 3 years. All 8 of them.