Syncing music to iphone6s

I have an iMac running 10.6.8 with iTunes version 11.4 (latest). I just got an iPhone 6S running IOS9. I would like to sync my music on my iMac to the iPhone. When I try to sync, message says my iTunes needs updating. When I try to update iTunes, it says I am up to date. I am at a loss. I would like to stay with OSX 10.6.8. What are my options?
Kevin

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