The latest Merlin release ( RT-AC68U_378.55_0.trx ) fixed my problem.
I have had the same problem ... AirPrint was not working. ( MDNS issues in Media Bridge Mode ? )
This setup below works fine for me ..
RT-AC68U as Main Wireless Router ( Merlin Fork from john9527 - RT-AC68U_3.0.0.4_374.43_2-13E1j9527.trx )
RT-AC68P in Media Bridge Mode using the 5GHz radio only. ( Merlin - RT-AC68U_378.55_0.trx )
Now AirPrint works like a charm.
I guess AirPlay will also work fine now ..
I was running a RT-AC87U (firmware Merlin Ver 378.55_0.trx), as a primary Router
And... a RT-AC68U (Same firmware ), in a bridge configuration.
It was working just fine for about 3 months, then I noticed my laptop, connected to the bridge via a docking station, was not getting an IP address assigned anymore. If I set a static IP address, I could see my network folders on another server, but could not get internet access. Sometimes, a hard reboot of the RT-AC68U (Bridge), would clear up the problem. Sometimes it would take a few re-boots and fiddling with the Ethernet adapter settings on the laptop, but it seemed the problem was getting worse everyday.
I work from home, and have two separate home offices(I have to use a bridge, since my commercial color-laserjet printer does not work via Wi-Fi. It's huge and has to stay downstairs). My laptop connects to the corporate system via VPN connection, through the bridge and through the primary router. (This is NOT part of the problem)
Anyway, I started to research, and even updated the firmware to (Merlin ver 380.57), on both the Router and bridge... Nothing seems to help. For now, I have to set a static IP address and static DNS server, to be able to get to teh internet. If I set the DNS server to "auto", I can see my network folders, so I know that the bridge portion is working, but I can't get to the internet.
My IPAD works fine, wirelessly through the primary router, adn another computer upstairs, hard-wired, works fine as well. It seems the primary router is OK. The problem is with the bridge. I'm convinced that this RT-AC68U in "Bridge Mode" is a "PIECE OF SH*T". I'm about to throw it in the trashcan, as my time is more valuable than just buying another, better, piece of equipment to work in bridge-mode.
Research is showing me that this is a known problem, with no fix in sight, since 2013. *sigh* I gotta find another way. I have too many webinars and on-line meetings to risk dropping a connection due to this crappy router in bridge mode.