Job and John,
Sorry for the ambiguity of my post. We are only using Nitris DX boxes on the 2008/9 Mac Pros. The 2013 Mac Pro is not using an I/O device. But the playback issue is quite bad on the 2008/9 Mac Pro and noticable but workable on the 2013. Both when running 8.0.0 (also tested 8.1 and same problem.) But again, when 6.5.4.4 installed, both systems play the media fine.