INTRODUCING A NEW KITTEN TO YOUR BIG CAT
Introducing a new kitten to your other cats can be a nightmare, and you need to be prepared for it. If you are a rescuer looking for homes for your babies, you need to be very careful about giving them to homes with other cats--not because the big guys are a threat, but because many owners can't handle the stress of the introduction and will return the babies to you and you'll need to start all over with your search. Prep yourself (if you are the adopter) or the adoptive family (if you are a rescuer) with descriptions of fiery hellishness, and everyone will be ready for what's (maybe) to come.
No matter how sweet and passive your catty is, he might react badly to the introduction of a little one to his territory and spoiledness. He might spit, scream, attack you, break things, hide, hit the baby, chase you around like he wants to kill you, move outside and refuse to come in, stop eating his fancy food, and generally just be a total jerk. Nasty Cat Time can last a day or a few weeks, but you will come out the other end, so just bear down and tough it out. It's worth it! It's so much fun having more than one cat, and more likely than not, the big nasty will be very happy to have a playmate once you've ignored his fits for long enough.
To make the introduction as smooth and scratch-free as possible, isolate the new baby in his own room and only let him out where you're home and watching the two to make sure big nasty doesn't try to kill tiny fluff. Little guy will be ok on his own for a while. Just set him up in the designated room with all his stuff and eventually the two will be able to officially move in together. A good way to safely introduce the two at close-range is to leave the baby in its cage in the middle of the house so that big nasty cat can approach him, smell him, and get used to him without any chasing and swatting. This method, combined with the isolation room, usually works well. As soon as you see that your cat isn't actually being aggressive (running away and hissing are fine), you can let the two work it out between them. They'll figure it out and develop a social order that makes sense, and soon enough they'll be best buds!
Good luck! Hope you don't need Band-Aids!