Andy and bmark,
Have you verified that syncing doesn't fix itself a few seconds into the track? Maybe even midway through the track? SC makes constant changes based on the buffer levels of all the various players.

Come to think of it, what is the memory buffer size in SlimRio? Does it report correctly to SC?

I did play around with the audio delay and start delay settings in SC, but I don't know if the audio delay values are device dependent or network dependent. One Receiver has 1000ms (over ethernet) and the other 250ms (over wifi).