Coincidentally i had problems getting my xingu from monsterfish to eat too when I first got it. It took almost a week to get him to even taste bloodworms. A few days past and he would finally pick at the floating bloodworms that other fish missed.
Its been a month if not more and he finally will go after a full cube, no shrimp or pellets yet.
I also refused to get live fish or anything for him. His only options were shrimp, frozen blood worms, or a variety of pellets. Just keep trying guys, trainer fish are very helpful.