and now you're having issues, wondering why it didn't work this way. So...now you have had 1 issue.
There was no music on the device once it was restored, but it would allow me to add it. When I tried to push the .ipsw file straight to the device to downgrade, without using DFU mode, the existing music did not show up, nor would it allow me to transfer music from iTunes to the phone (iTunes would show the music greyed out, device showed blank). DFU mode to factory default, and restoring from backup cleared that up.