This is insanely frustrating. I received a DIR-825 from comcast to help beta test IPv6. Prior to this, I had a Netgear setup without any issues.
My problem is this: Randomly, the DIR-825 will prohibit streaming to my AirPort Express via AirTunes. It'll also disappear from Bonjour Browser and AirPort Utility. I can connect directly to it, if I enter the IP into the AirPort utility directly.
The only way to get it to come back is to either reboot the DIR-825, reboot the AE, or unplug the ethernet to the AE.
I've also tried configuring the AirPort Express to connect wirelessly, but the same problem occurs.
If I plug my laptop into the back of the DIR-825, I have no issues streaming. If it stops over wireless, I can plug in and access the AirPort Express without any issues. The DIR-825 and the AE are on the latest firmware. I can ping the IP of the AirPort Express when the streaming drops out and it responds. Nothing interesting at all in the logs of either devices. The AirPort Express just says "AirTunes stream from X stopped."
It *appears* that the DIR-825 is killing Bonjour/mDNS traffic over the wireless, for some reason. There are other (unanswered) threads about this. (see: http://forums.dlink.com/index.php?topic=11045.0 and http://forums.dlink.com/index.php?topic=16058.0) I know it's a pretty rare setup, but it's incredibly frustrating to me. I have to pick between wanting to use IPv6 and having a functioning AirTunes.