You do not need to back up the native firmware.
What you can install is a dual-boot system, that preserves the native firmware, and allows you to choose to boot up in native Firmware, or Dingux.
The same system allows you to later flash back to just native firmware (that is, get rid of Dingux if you want...but who'd want to...)
Have a look at this link, and follow the guide completely, and you shopuld be flying Dingux in no time. I'm a complete moron when it comes to this stuff and I was able to flash my Dingoo with the dual boot installer using this guide...
"The complete Idiot's Guide To Installing Dingux"http://www.dingoo-scene.com/TheCompleteidiotsGuidetoDinguxWindoze.htm
One thing, though...if possible, try to use a computer running XP to do this...some Vista users did report problems. and I know nothing about those running Windows 7. Just use a compy that runs XP if you can.
If I have helped you today, please give me karma, thanks.