So far, we are very, very pleased with how existing cat and new kitten are getting along. Our only previous attempt to introduce a kitten to an existing situation went poorly, when our old female cat attacked the newcomer so badly I had to separate them, although not quickly enough to keep me and the kitten from bleeding.
I would say Reuben shows about 60% indifference, 30% tolerant interaction, and 10% annoyance. Not anger...just...well, kind of like my kids: the kitten will bounce up, and Reuben will respond, and play a bit, but he gets bored/tired after about 30 seconds, while the kitten wants to keep playing, at which point he bats at her(or near her...she is too quick for him) half-heartedly, then lays down and ignores her.
This afternoon, he was sleeping under the chair in the living room, when Dahlia came over and started rubbing on him. He responded by basically giving her a bath.
She accepted this for about a minute and a half, before she seemed to want to get away. Reuben wasn't done though, and used his right leg(which weighs more than she does) to pin her down until he was done.
I've seen mother cat's give their babies a bath like this, but didn't know this was something any adult cat would do for a youngin'. Whether this was out of affection, a teaching moment, or to get the smell of Humane Society off her, I'm not sure.
Of course, as I told my wife, Reuben and I are kind of the same...old, fat, fixed males...if my wife brought home a sweet young human female(not too young, you perverts) I would probably attempt to give her a bath too....
The final option, given the size difference, is that Reuben was sizing her up for dinner tonight...