The "Play/Pause" thing is a known issue with PT9 and is probably nothing to do with your interface. Most have found that you can (temporarily) get rid of it by changing the buffer size in the Playback Engine dialogue to something else, then switching it back. If that doesn't work, trashing Pro Tools Prefs and Databases fixed it for me.
Here's the appropriate thread to have a look at:
http://duc.avid.com/showthread.php?t=306153