I created a Windows 7 virtual machine on my Mac, downloaded and installed iTunes 10.5, when I launch it with my dad's iPad plugged in, it says it can't access the iPhone update server and therefore, I can't access the iPad. I tried with and without TinyUmbrella (program which helps downgrade iOS devices) with no luck. And on my Mac, I can't downgrade iTunes as I'm on the latest OS X version (10.9). I will try again later or tomorrow but it looks like a dead end. Our luck would be if someone has a 1st gen iPad, which is now obsolete, but its maximum iOS version is iOS 5.1.1, exactly the one we're trying to downgrade to.