I have a TiVo Roamio Pro and a TiVo Premiere on my network. The two TiVos are connected separately to my home network via TP-Link MR3020s set up as wireless bridges.
Originally neither TiVo could see each other. However, on the Roamio, when I went to Apps & Games, selected 'Add an App', and then put in the IP address of the other TiVo, the Roamio can now reliably see the Premiere.
However, this doesn't work on the Premiere. Here's what I've tried doing, and troubleshooting steps I've taken.
Loaded up 'Bonjour Browser' on both a wired and a wireless computer on my network. Both computers see both TiVos. Ran a tcpdump from my wireless access point running Tomato to monitor UDP traffic coming from both TiVo boxes. Both TiVos are sending the appropriate mDNS packets advertising their services, and I can see the Roamio and Premiere communicating back and forth.
Also tried rebooting both boxes multiple times, and also disconnecting/reconnecting the cable to force DHCP release/renews (even though my gateway reassigns them the same IP address every time). No change.
If this helps, pfsense is my primary gateway, and I am running Avahi so that my computers can discover my NAS and other servers located in a different subnet.