I can also confirm that for the last 3 years I've also had so much stuttering that there's actually more silence than music in the transmission.
And this only happens when the device *sending* the music is on a 5GHz wireless network.
When I switch my Mac (which is transmitting music from iTunes) to my 2.4GHz network, everything's fine. When I send music from my iPhone (which is connected via the 2.4GHz network), everything's fine (well, aside from the 'popping' issue described here: https://discussions.apple.com/thread/2651422?start=0&tstart=0).
I tried Derek's fix of disabling IPv6. However, now I can't play anything at all, & I get the following error message in iTunes: "An error occurred while connecting to the AirPlay device “HTR-4065 92BDE8”. The network connection timed out." Switch my Mac to the 2.4GHz network, everything works fine again.
Crazy thing is-- I've had this problem over the last 3 years now. In that time, I've swapped out the Airport Express, gone through 2 more 'main' routers in my home, 2 new Macbook Pros, a whole new receiver + speaker system, etc. And the problem's still there.
That strongly suggests that Airplay is the culprit. I'm surprised this problem isn't more widely reported (at least it is here in this thread), especially with the wider adoption of Wireless-N (we're going to AC soon...). More surprising is that it appears Apple hasn't done anything to resolve it in 3 years.