Tough call. Not recommendable, but assuming there are a lot of rocks to break up territories, and you're going to do a ton of water changes, I think it could be made to work in either tank(the 46 probably only if you got rid of the other fish). Keep the fish well fed and keep the water clean, and adding 12 of those would probably be okay. I would sooner put them in the 75 because its a 4-foot tank, but the 46 is probably better for them, because with a group of 12, there probably won't be any single fish on the bottom of the pecking order, so they'll all take a little aggression here and there, but it would probably work out. In the 75, the demasoni might go after other species and not keep to themselves. Tough call, definitely feasible, but certainly not without risk. You're starting to push the bioload limits, but w/ regular water changes, you'll just have to keep an eye on aggression. Good luck with whatever you decide.