IP of your PC is the IP which is shown in the router. For example:
you assign 192.168.0.33 for your PC
your router IP is 192.168.0.1
you assign 192.168.0.34 for your Dreambox (or whatever receiver)
These IPs (PC and Dreambox) are assigned manually.
First time, when you just switch your DM on, you have to long press Switch ON/Off button in order DM gets IP automatically.
So, if your DM was assigned 192.168.0.33 (for example), your PC IP must be 192.168.0.34 (also, for example).
Consequently, you must know your both IPs and add them to the router settings.
In the DCC (dreambox control center - available in Dreambox utilities), to connect DM with router and further with PC and for further manipulations with DM settings, you must also manually to enter the IPs assigned to the corresponding windows. You will see it in the schematic diagram of DCC - the links will become green if the connection is right.
After this, you will set up your mg_cfg file (entering 192.168.0.33 as IP of your PC to the L {..} parameter, leaving 514 port unchanged.
In the 3Csys... settings window, you will enter either 192.168.0.33 or 192.168.0.34 (i asked you to play with IP settings), restart DM and finally you will see the lines running in the main 3CSys window. That's all.
You may install Gemini firmware, as it is the best one. Only one thing you have to find is that the imapge must contain built-in emulator (mgcamd), cause Enigma does not support emulators any more.