this is a damn good question, so here goes my imagination:
Cichla monos and temensis: they like to be in groups, so i'd have about 10 of each in here
leopoldis, motoros, and those tiger rays... i'd have about a dozen rays in total.
tigrinus catfish... a dozen or so of these
Tiger shovelnose and RTC: 2 of each...
silver and black aros: 4 in total, I feel when you have too many they don't look as good... too many fish patrolling the surface and then you can't really concentrate on any one to appreciate their "pissa-ness" (i made that word up, im from boston, and I didnt wanna say "beauty" because that sounds fruity)
2 pairs of paired off green terrors
a shoal of 100 bleeding heart tetras: the new england aquarium has these fish in with large cichlids and other predatory fish. id just keep my fish well-fed to keep them from picking these guys off... which probably wont work but i have a blank check so i can do whatever i damn well please
10 red tailed barracudas: full grown and on the prowl... these guys would be unreal and would be able to attain their full length of a foot and a half, which should keep them from getting swallowed.
assortment of plecos: gotta have garbage men but I wouldnt have too many because they might bother the rays
a pair of Amazon yellow-spotted turtles