My new AirPort Express is dropping its digital AirPlay output
I have a home network w/ a TimeCapsule base station and two AirPort Express satellites. One Express is the 'latest' (AppleTV-alike) and the other is the 'next-to-latest' b/g/n (wall-wart) model.
Everything is up-to-date firmware-wise, and software-wise as of the moments I am typing this. (I'm a developer and have also tested 10.8.1 prerelease 1 against this problem to no avail, fwiw.)
The problem is this- when the 'new' Express is connected digitally to my stereo (via optical -> Schiit Bifrost D/A) I experience rather persistent drop-outs of the digital stream when using AirPlay via iTunes. (It happens with other output also, fwiw, but thought I'd constrain the problem a little for the sake of debuggery.)
This is especially noticable since the Schiit doesn't use the DAC's mute line and, instead, drops a relay whenever the digital signal flakes out. Thus, I hear a reassuring 'click' when the Schiit (you can tell I love typing that, right?) acquires and loses the digital signal. (Note also that I've tried this with an older DAC I have and have the same results, just no 'click' of reassurance... only a meager LED.)
If I replace the 'new' Express with the 'almost-new-wall-wart' express this problem goes away- poof! Nice smoove sound. No dropouts, nothing but the AirPlay music of my choice. (A few minutes ago, Lisa Germano... right now, some free jazz, because I need a headache.)
I've tried most of the usual troubleshooting things- different inputs (swapping the two different airports), different digital cable, different DACs, and even a little bit of different source delivery (right now, a Retina MBP, and sometimes an iPad.) The only thing that -seems- to matter is the model of the AirPort Express.
One interesting thing I have noticed is that, when using AirPlay I'm getting a rather constant 150-or-so KB/sec upstream according to Activity Monitor. Makes sense I suppose. When these glitches take place, I see a big ol' 'spike' to like 250 KB/sec or so, then, the music will 'start over'. The drops are about 1-2 secs and usually the music stream 'picks up' where it dropped off, but usually is then choppy until everything catches up. (Buffer corruption perchance?)
Thoughts? I realize this is a really complicated setup issue, and there might be 1-2 other hu-mans on earth with this same setup, so any corroborating evidence would be welcome. I'm going to drop a note to my ol' pals at Schiit (man I love typing that) to see if they see any of this too.
AirPort Express [New]-OTHER, OS X Mountain Lion