Wow, that's a good size. Personally, the only amphilophus I'd keep with geos would be Robertsonis. I am not sure about Isletas but I think if they are anything like midas, then the geos would be in for a rough ride. I've kept different types of midas and all of them are pretty rough, although mixing with Parachromis and nandopsis IMO is okay. However, IMO, they are not suitable for an earth eater tank. They're fast on the move, and tends to be inquisitive in an intrusive way, whereas geos are generally a peaceful and slow moving type of fish.