How to install OpenWRT on German EasyBox 804?

Hello, i'd like to turn my old EasyBox 804 into a little managed switch with some more things with OpenWRT. I found the page of the device (Vox 2.5), but im unable to flash the factory or sysupgrade image on the OEM GUI because it says the file is invalid. In the bottom of the page is some OpenRG stuff, but i do not understand it. Can someone help me with this? Or is the German EasyBox 804 just unable to use with OpenWRT?

You mean https://openwrt.org/toh/vodafone/vodafone_station_revolution?
Depends on the board variant. Which one do you have? Even if you have SHG2500, it is Broadcom. Dead end, I would dump it, not worth any work on it...

Just my 0,02€

Yeah its the SHG2500, with the German Vodafone OEM Firmware. When i try to update from the .img file it just says that its invalid.

I don't need WiFi or DSL, i just want to have a switch that can route.

You may want to shorten the filename before upload to something like firmware.img or so. Sometimes, the OEM GUI can´t handle long filenames proper.

Tried that, i tried changing to .rms but that just failed.
I also tried these OEM Firmware Versions: 3.02, 2.5, 5.02

I guess it has to be in the .rms format for it to accept it. As specifically mentioned for the SHG2500 from Germany on the Wiki, i just dont know how to properly convert it.