I'm having the same problem. I was able to connect the HDHomerun to my windows laptop ethernet port, and it worked fine. But if I try the same thing on the backend ethernet port it isn't detected. I'm running Ubuntu 12.04 with mythtv installed.
I tried setting up the wired connection as Manual using the ip address/netmask suggested here:
but no luck. I tried setting the connection method to Link-Local Only, but again no luck.
In both cases,
says no devices found. The Hdhomerun is showing the blinking green LED, indicating its waiting for a DHCP lease. The Network Connections window says that that wired connection has never been used. I read through this thread:
but no luck.
I've read that it may be necessary to install a DHCP server on the mythbox in order to make the connection work, but I couldn't get any details on if that was true or not.
You mentioned that you searched through forums for solutions, so I don't know if any of this information was new for you, but maybe it can help. If you do figure it out, I'm looking for a solution, too.