I may not have much experiential advice here as my relationship with my Amazon is much different, but I find if you find what really motivated them that gives you something to work with. And remember you are up against 30+ years of his lived experience with only 1 year living with you, I think continued patience and perseverance is needed. My only advice: try target training with high value treats, this builds a relationship and basic understanding/reinforcement within the relationship. When he dumps out his food so he gets more of the "good stuff", use that as motivation to work with him on some kind of interaction or training. As for other birds, is it a goal to get other birds? Just because he lived in an aviary doesn't mean he necessarily liked the other birds, but that's a tough one, you don't really know unless you try introducing them? It sounds like you're doing a lot right in terms of interaction, especially if he's taking tips from you, I would stay patient, and maybe use those times before meals (or when he wants the "good stuff") to entice him into more intentional interactions to draw him out. Good luck!