Supernait + Airport Express = 1/2 second dropout at 5 seconds into audio stream

Hello,
I've got a problem with streaming audio via an airport express (via itunes) to a supernait via an optical cable.
Consistently, at the 5-6 second mark into a stream (song) the audio drops for about a half second then recovers. The rest of the stream plays without interruption until a new stream is created for the next song then it repeats at the same point.
My suspicion at this point is that it is something that the supernait is doing, due to:

1. Occurs when either of my two Airport Express devices when plugged into the supernait via an optical cable (removing AE issue).

2. Occurs when AE is cabled directly to the mac with wireless turned off (removing wireless issues).

3. Occurs on multiple source Macs, both desktop and laptop (removing some issue with the individual source computer.)

4. Streaming via AE to a Yamaha AV amp via same optical config does not have any dropouts. (again, attempting to remove AE issue)

5. When playing to both internal computer, and SN via AE, the internal speaker continues to play the stream whilst the SN/AE drops out and recovers at the same 5-6 second mark.

6. There are no dropouts when directly connecting the mac to the SN via an optical cable – in fact this is how I’ve had it configured for the past year. Its just now I’ve moved the SN further from the computer than the optical cable can reach.

Any ideas? Has anyone else experienced this issue?

Matt