As I type "Mr Jinx" (see story of name at the end of the message) is sitting on a file cabinet next to my computer desk, sleeping. He's been allowed to wander free today with supervision of course. My cats are barely curious of him, and less so now that there isn't a door separating them. (The kittens were camping outside the door of the bedroom he's been staying in). He's the only cat in the room. He seems very content. When the other cats get too close, he growls, and there has been a hiss here or there, but none of them have even batted at each other. So far so good.
I appreciate the suggestions about introducing a cat to a household and I'm sure they work very well, but I think it's going well so far and it will be awhile before they're left alone-- and I'm not going to be keeping them 100% isolated. I'm always right up next to Mr Jinx when he gets nervous, petting him and trying to show him he's safe and protected, and he seems to understand that because the couple of times he's felt theratened I've come and sat or lied down next to him and he ends up relaxing and stops the growling, etc.
On a sidenote, his original name happened to be the same name as my 15 year old sister, so there is no way we could keep it. Except for not having hair quite as long, he looks almost exactly like Mr. Jinx from Meet the Parents (black tail and all), so that's what we've decided on. He's a big lazy old cat, a real sweetheart