It sounds like Rockbox wants to see a copy of the SanDisk firmware file, fuzeA.bin . “Original” is to distinguish it from the Rockbox firmware, not to have the earliest version. That is SanDisk’s copyrighted firmware, so Rockbox would get in trouble if it put the SanDisk firmware in its automatic package. .
You can get the Sansa firmware by finding what version your hardware is (under Info, see if your firmware version begins with 1.x or 2.x) and downloading the All Regions link for your version. Ah, you have a v2. So get the 2.x Firmware
It’s a zip file. Unzip it, take fuzea.bin and drag-and-drop it onto the driveletter that says Sansa Fuze in Windows Explorer (Computer or My Computer). Your Fuze will update again when you disconnect.
Rockbox is really not for people who want everything to be automatic. You have to be willing to change settings, debug things, etc. It’s for computer geeks. There’s a lot of information at www.rockbox.org and they have their own forum. But you are going to have to think about how the software works, and if you don’t want to do that, stick with the original Sansa firmware.