Our male quaker used to be very cage aggressive (especially when his mate was living with him - she is now passed). We used to just leave their door open, they would come out, and we could easily pick them up. His adjustment to the death of his mate took about 4 months, and even with his door open he would never come out. I missed him so much and got sick of him being a depressed little boy, so I started trying to get him out from inside his cage. When I put my hand in for a step-up, he would bite if you got near him. He would be upset if there was a hand in the cage, but wouldn't lunge toward the hand until it was close to him, which was a good thing and helped with the training. He KNOWS what "step up" means, which also helped. I would put my hand in his cage, say "step-up.....step-up....step-up" repeatedly while not reacting to his lunges or bites. I started far from him and moved my hand closer as we progressed. I would switch between many cheerful-toned "step-up's" and a more menacing "you better step-up" tone. I wouldn't give up until he stepped up and I never let him or his lunging/biting attitude win. After about a week of doing this every day, the time it took for him to take me seriously drastically shortened. Now he steps up from inside his cage without a problem. Well, most of the time - sometimes I have to go back to the menacing tone to get him up but then he will listen right away. No more bites, though. It is my proudest training - really the only behavioral training I have done.
In my case, Oscar is a bit of a timid, nervous bird (not a huge cuddler), at the same time aggressive and defensive. This worked in my favor as the bites were never too too bad and he never all out attacked a hand.
Good luck!