Just an update to this, I contacted Bitmain and they provided the same info as RichBC with a last step:
"After you prepare microSD with image put it in the slot of your computer and then switchthe S5 firmware with the S7 firmware ." which I havn't been able to figure out yet. I'm going to try and boot my controller with the S5 firmware and see if I can upgrade the firmware from there.
I think the reason for this approach is that there is not an S7 Image available. So you load an S5 image via the microSD & then if you are up and running use the built in firmware upgrade tab to load the corrrect S7 firmware?
Rich