Iphone 6s won't sync to Itunes?

I have a Macbook Pro that I got back in 2010. I'm currently using Mac OS X version 10.6.8. I know there have been major updates since my computers debut, however, this was my first Mac so I'm in no means tech savvy to know what's up!

Anywho, my Itunes is currently running 11.4. I'm currently using the Iphone 6 and using the 9.1 software. For all the previous new software updates that Apple has been making for the Iphones, I always update through my phone and not my computer. I have never had an issue after updating my software and connecting and syncing to my Itunes. I just backed up my iphone 6 to my Itunes a few moments ago.

Now my question is why is my new Iphone 6s plus not syncing to my Itunes. It is letting me know that i need to download Itunes 12.3.1 for OS X. From what I have been reading on other posts is that the new Itunes 12.3.1 is not compatible with an outdated Macbook like mine. So does that mean that I will not be able to download the new version of Itunes, which will leave me unable to sync my new Iphone to my Itunes? How does any of this makes sense? The thing that really confuses me is that my Itunes allows me to sync my current phone which is running the 9.1 software to my Itunes 11.4?

If someone could please share some insight, that would be greatly appreciated! Am I going to have to choose between my 3,200 songs and well develop Itunes or a new Iphone 6s which I will have to start from scratch?

Well you basically need to update that to yosemite

Your Macbook is not outdated it just needs updating. Go to the App Store on your Mac and update to El Capitan - this is the latest version of OS X (10.11.1) which will give you all the latest goodness and will update iTunes to the latest version too.

See…

http://www.apple.com/...o-upgrade/

It will take a while (hour or two) to update so leave it to do its thing and wait for it to restart itself after the update.

I have a MacBook Pro Mid 2010 that has BOTH OS 10.6.8 and 10.9.5 installed (three partitions). In OS 10.6.8, no sync. In OS 10.9.5, sync.

You can see here--> http://www.apple.com/...-6s/specs/ what is needed:

"Syncing with iTunes on a Mac or PC requires:

Mac: OS X v10.8.5 or later
PC: Windows 7 or later
iTunes 12.3 or later"

EDIT:

The answer to "Do I need to backup my precious files?" is ALWAYS "YES", no matter whether you want to install an upgrade or not.