A group of M. thoracata could definitely work, my four were in my Rio240 until yesterday, when I moved them down to the 5x2x2 to let them recover from the malicious nipping on my S. tinanti duo. When they get to breeding age, two male Hoplos can apparently fight to the death, so do try and sex them in the shop to get a mostly female hareem. Males have longer pectoral fins that turn orangey red as they get bigger, plus when looking at the fish from underneath, males have two "shield" plates almost in line with their pectoral fins that nearly touch whereas females have a huge central gap between them.
"Mattlee" will be able to give you first hand experience of Thorichthys aureus, he had a group until quite recently.
I'd amagine a group of CA dithers would work pretty well with the Hoplos and cichlids, providing they are confident at feeding time and reach a decent size so as not to be considered "live lunch" by the cichlids.
Please don't take this as a hard sell, but I have ~29 Ilyodon xantusi (a biggish Central American livebearer, considered to be decent tankmates for hardwater cichlids) and 48 Steatocranus casuarius (African Blockhead/Lionhead Cichlid) youngsters looking for new homes, born and raised in our local tap water. If they are intrest, give me a shout.
Edit: Hmm, maybe it was not Mattlee that had the T. aureus, nothing obvious is coming up in a forum search. Perhaps my memory is playing tricks on me again!
