Hi ahud,Adam,
You are making me want to add either a pair of Thorichthys or Crytpoheros to my 125g. So what are you deciding to go with?
My personal opinion is that 2 Thorichthys is not ideal. They like to shoal, not a schooling fish per se but very social. Check out some of Darren's threads where he shows his Thorichthys spawning inches apart from each other.
My current state of mind is I will swap the gravel and keep all the fish, but I will reduce my mixteco numbers down to 9 or 10. The 4 or 5 mixtecos I move will be going to cichlidfish assuming he can make it to my house. I'm off this Friday, so I'm planning to break everything down then.
I'm also going to be adding a school of livebearers, species TBD. I'll post more about that later, would like some input.