How to prepare combined front/backend for remote frontend?

I've been ruing MythTV as a combined front/backend for almost ten years, but now I have a RPi2 and an Android tablet which I would like to run frontends on. I have the tablet ready to go already.

I have configured my router so the backend machine now has a static network address, but when I set mysql to accept network coections from within MCC with 0000 as the key on the backend. Unfortunately, doing this somehow stops me from being able to coect the frontend to the backend on the local machine and the remote frontend also does not work.

Any ideas what I'm doing wrong?