Convert Coax Internet Signal without modem to RJ45 - eviltoast

Hello,

I want to build my own router because the current one I have is missing some features I require (like netboot for example). The only problem I have found so far is that I need some way to convert my incoming coax/cable signal to rj45 because I want to fully discard the old router as it is only taking up space. I know that MoCa exists, but as far as I know, that is only used to convert an existing rj45 to coax, or am I wrong?

The current setup is like this:
Incoming Cable --> Fritzbox 6660 Cable --> all other devices

and I want to change it to:

Incoming Cable --> some kind of converter --> my router --> all other devices

Any help is appreciated