I foster and have 2 resident cats, so I do introductions a few times per year. I highly recommend Jackson Galaxy's guide. I've linked part 1, but there's 5 parts, the rest are linked within. It's worth reading the entire thing, because he does a great job of explaining why he recommends each step, which is helpful if you need to modify things a bit.
You need to figure out a room in your house that can be The Boy's basecamp. This is where The Boy is going to spend most of his time until Anya can tolerate him, and hopefully isn't a "high value" space for Anya. Without knowing either cat, I'd say you should plan for a minimum of 2 weeks of very carefully managing the process of introducing them to each other, and probably at least a month before things really settle in.
Also, make sure The Boy gets neutered ASAP, if he isn't already!