Likewise, I have a Yamaha RX-V473 which plays music via airplay from iPhone/iPad without problems. Since I upgraded my Mini to Mavericks (now 10.9.3) the iTunes airplay to the Yamaha is intermittent and after a song or so it gives up and shows an exclamation mark in iTunes on the Mini.
I eliminated the problem by doing two things (all from other recommendations):
Created a /etc/sysctl.conf file containing the line: net.link.ether.inet.arp_unicast_lim: 5 -> 0
Disabled IPv6 on the ethernet interface by using the command: networksetup -setv6off Ethernet
I was very pleased to have my music back but (as I now learn Bonjour needs IPv6) now my iPhones will not sync to iTunes remotely (wifi to the ethernet interface via a router - the Mac Mini wifi interface is disabled). If I re-enable IPv6 the airplay bombs out but the iPhone sync works!
All airplay music and syncing via wifi worked fine before the Mavericks upgrade. Needless to say, airplay to an airport express device was not affected by the upgrade, just the Yamaha. I'm pretty annoyed to have to delve into the unix commands to fix something like this. The reason I bought a mac was to NOT have to fiddle about for hours troubleshooting. Combined with "beach-balling" my iTunes often, I think the networking in Mavericks is gash with SMB problems and spurious ARP broadcasts. There's nothing wrong with Yamaha's implementation of airplay and there is nothing wrong with my network set up. So now I have to contemplate a roll-back or more hours of troubleshooting. Apple, ***?