If you are looking for an actual solution - I guess you could start Windows 10 in a VM(MS provides free images for testing purposes), install latest iTunes on it so you could upgrade your phone to iOS 9, then continue using your mac and its version of iTunes.<p>By the way - El Capitan supports mid-2007 iMacs:
<a href="http:&#x2F;&#x2F;www.gottabemobile.com&#x2F;2015&#x2F;10&#x2F;04&#x2F;os-x-el-capitan-on-older-mac&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.gottabemobile.com&#x2F;2015&#x2F;10&#x2F;04&#x2F;os-x-el-capitan-on-o...</a>