Some advice from someone who got the cichlid bug and started mixing them: you will always have a dominant fish.
Every time you add a new cichlid the established ones will try to challenge it to determine where it belongs in the dominance hierarchy. If your texas was much bigger than the africans then it shouldn't be a problem. Also, you can select a more-peaceful cichlid to be your "dominant" fish (depending on species and individual personality). If it is the biggest then few will mess with it and if it's peaceful it won't mess with others on a regular basis. I have also seen people keep africans with large flowerhorns because the flowerhorn will never catch them (dither cichlids).
Now when I first started trying cichlids I stocked a 55g with too many cichlids (all juvenile) including: jewel cichlids, an oscar, a salvini, a mayan, green terror, jack dempsey, and maybe another I'm forgetting. As juveniles they are all pretty okay, but once a cichlid reaches sexual maturity you will see its true temperament. My male salvini was the dominant fish. It was the largest, held the best territory, and would never lose a fight. However, it would never pick a fight. The same was true with my JD after I moved my salvini to another tank (spawned him). Other species and individuals may behave differently. My oscar never picked a fight and would lose to jewel cichlids half his size. Nobody messed with any eel-shaped fish though (e.g. spiny eels, bichirs).
What stops an ***hole cichlid from being so bad is a worse cichlid. You are already seeing this. If your texas is a big, bad, butthead when he isn't being dominated, then your best bet is to find something noticeably larger than him or smaller than him so nobody has to fight to determine who's stronger. it's when cichlids are of similar size and strength that they fight most. I would either select a large, more-peaceful cichlid (but capable in a fight), smaller cichlids, or fish other than cichlids to go with the texas.
I hope some of this information will keep you from having to learn the hard way. This is just my experience, and fishkeeping is an experience-based hobby. I hope others will weigh in on whether they agree with this info or if they have had different experiences. Best of luck and remember: this happens to every cichlid keeper. Many of us have had to use eggcrate to divide our tanks and separate aggressive fish!