Well hello to you! Safe and sound here, and you?
To start off with, greys are very inquisitive creatures. They study things that sparks their interests. They usually don't take no for an answer.
If they choose to do something, they're going to do it. I have a grey, a tag, but none the less same attitude as a cag. And had 2 others in past, tag and cag. Old age took them.
There's a lot of good advice here in this thread, so don't be shy to try it all. Because what works for one, may not work for another. Thing about a grey, they are thinkers, they'll try to outsmart you.
I'm not kidding.
In your case, he's biting mainly because your taking away his "fun". His way of saying " go way
I'm having fun here. "
What breaks those habits is to find similar items to draw his attention. For example, my grey has this annoying habit of attacking phone when it rings. Goes mental on it. Sooooo, I found this toy phone in thrift store that looks similar. What fun he has now. Leather sofa, lol...I have same problem... I went to hobby lobby and got a sheet of leather and made a mini sofa... ( trust me it looks like crap, I'm no furniture maker) it's a couple feet wide. He chews that till he gets bored.
I would also invest in a couple more perches or play stands. One is never enough with a grey.
I have 7.. 2 of those are play gyms. Why? Because a grey likes to fly from one to the other. Because if you don't, they'll start landing on lamp shades, your flat screen tv, or whatever. The biting will stop once you introduce more fun things. Get a large Tupperware tub, a foot by a foot and fill it with all your used toys of your grey, even safe plastic. Place near or in his gym/ perch. They'll go to it.
Try a paper grocery bag, put toys or plastic golf balls in it... Grey's love that. They're like a cat when it comes to that. Wad up paper, place it in cage or perch...Grey's love playing catch with paper balls.
Hope this helps....