I did something similar, but with small change and it all worked. I just have one Mac in the office, an older Mini that cannot upgrade past Snow Leopard. I'd always had it as my music/media box, so just kept it for that use.
Anyway, I had upgraded my iPhone 4s to 9 successfully and still synced with iTunes 11.4. It was that last update to 9.0.1 that killed it for 10.6.8/11.4.
Installed latest iTunes on a Win 7 machine, then successfully synced 4s to it. Then did the downgrade back to iOS 8 on the Windows machine.
Now I was able to talk to the Mac again and do a full restore there. Thanks to this "near death" experience, I'm moving all my media stuff to a Win7 machine.
Been using Macs since the early 90s, but looks like I'm done with it now.
All it would have taken was a simple notice that the iOS update to 9.0.1 being pushed by iTunes and iPhone, would not be compatible with my version of OS X and iTunes. Then I would have probably bought a newer Mini and stayed on the bus.