Re: Has anyone experienced...
Welcome, and I've sort of had that happen.
We are a multi-cat household (6-12 at any given time) and sometimes that number is bumped up when I foster litters of kittens. Most of my cats are very good about accepting newcomers and kittens seem to get an even more lenient "pass" because of their age. Have you only had the new kitten a short time? IME, it can take a few days to up to a few weeks, or even months before everyone gets adjusted, but they have all adjusted. Some, came right in and were right at home and accepted by the established clan immediately; Bonnie, Blaze, Marmalade, Reilly, Squirrely-Jo, Shasta, LuckyDuck, Dusty and Floofy come to mind.
Wow. That list is long! I guess I've just happened to luck into getting very laid back cats?
Anyhow, give your two time and I'm sure they'll get along just fine. It seems like your big boy is very accepting and THAT is the key to getting cats to accept other cats; when the established cat 'okays' the newcomer. I feel eventually the newcomer will come around and become accepting, especially if your big boy doesn't give up wanting to be friendly. You could try giving them treats near each other and playing with toys that keep them entertained and sort of close together; like DaBird or Cat Charmers and lazer lights.