A good news report. I use AJA io XT on my 2012 MacBook Pro, with Final Cut Pro 7.0.3 and Mac OS X Mountain Lion 10.8.4 and have had the audio distortion when stopping/starting playback issues since purchase.
The combination of the new 10.4.5 drivers, and the 4/26/2013 firmware has not only stopped the audio issue but even made my second monitor, which is daisy chained through the io XT more reliable. I cannot tell you how much this relieves me. A very happy camper.