Most people discourage starting the bonding process when one of the rabbits isn't neutered. You can start the process by just exchanging the new bun's scent with your other buns, but I would hold off the face to face meetings until he is neutered. You might be okay with the female but I wouldn't try the male until after the new one's altered.
Bonding a male with a male is possible, but it's a lot harder than bonding a male and female. I would really make sure that you research this and make a set plan on how you're going to bond them, just so that you make sure you do everything properly. I would keep the male separate for a good month or so before any face to face meetings between the others, and just work on getting the male and female used to his scent first.
I would also try to bond them one at a time, probably starting with the new male and the female, especially when the male hasn't been neutered yet. This is for the face to face meetings, but you can get both of them accustomed to his scent with towels or 'decoys' (a stuffed rabbit toy that you leave in the new bun's cage for a while so it gets his scent).
Here's some websites that have a few ideas on how to bond rabbits:
http://www.rabbit.org/faq/sections/introductions.html
http://www.myhouserabbit.com/tip_multiple.php