Same issues. I've troubleshot Apple TV / iTunes Airplay so many times, I feel like I have a (terrible) part time I.T. job. It's unbelievably random what will SOMETIMES work to get it working - and even then it's often only temporary.
Here's the biggest bee in my bonnet, and why I know there's nothing wrong with my router: I can stream HD video from Netflix, Hulu, etc., JUST FINE to Apple TV, very seldom have any problems (not counting Apple TV's horrible fwd / rwd navigation.) Consider the fact these are HD video files coming off satellites, originating from god knows where. Now consider that I have no consistent control whatsoever over streaming an mp3 audio file I OWN, living on MY HARD Drive, from iTunes to the Apple TV, literally 20 feet away from my iMac and router. iTunes is Apple flagship software for all its media, and trying to connect all my iProducts with it is the glitchiest most unreliable thing in the world.
When are they going to wake up and give a crud about this? If only I could see MY music as reliably as I see the lastest Top 40 garbage Apple vomits on the top of my screen with "Music" selected. Gosh that would be refreshing.
Apple: Think Indifferent!