Sounds like lag time might be doing it.
Like some kind of network lag time?
I have similar behavior here pushing music from the PC to the Onkyo. Pause and play are instant, which seems like if it were network related would have a lag also. I have a suspicion that the gap is being caused at the stereo, but I don't really know. I hope that it is something that can be overcome though, because those inserted gaps really interrupt a listening experience.
Edited to add:
I have now done some research into the Onkyo receivers, and I have found that they do not support gapless playback. So for my setup I suspect this flaw in design with my stereo holds the blame. Too bad, as I don't think Onkyo has any interest in doing a firmware update to support it.