I have a very similar problem. I wonder if I could get some advice.
I have a Billion 7401VGP, which I use primarily as a router. This is connected via Ethernet to an Airport Time Machine, which acts as my primary wifi network device. I have 4 Macs and a phone connected to the wifi. My media lives on an external HD which is connected to the Time Machine via Ethernet.
I bought an ATV for the purpose of serving media from the external HD via Plexconnect to the ATV.
I followed the steps by manually setting a fixed DNS on my iMac, and installed PlexConnect on it. I set the ATV to manually see this DNS in the ATV settings. This resulted in not internet access on the ATV, including no Plex through the Trailers app.
I read this thread, and I copied those things that worked for Arachne17. I changed the router IP and I unchecked "Use the router as a DNS server". These did not work for me, and I am still without internet access via ATV.
Is there anything else I should be trying? I am not strong on network admin, but I can follow instructions.
Thanks