Tips that made my CS5.5 and BMD play smooth are:
Issue
When you try to play audio or video files in Soundbooth or Adobe Premiere Pro, playback stops or loops after a very short time—from a few frames to a few seconds.
Solution
Do one of the following:
• Remove the Aggregate Devices plist file.
1. Open the Finder and navigate to /YOUR_HD/Library/Preferences.
2. Rename the com.apple.audio.AggregateDevices.plist file, or move it to the trash.
3. Restart Soundbooth or Adobe Premiere Pro and retry.
4.
Audio tracks in premiere are stereo or mono. And you can only edit like tracks to like tracks. Your A1 track is stereo and your source is 2 channel mono.
To get fcp like behavior, check your new sequence properties audio tab and change it to 0 stereo tracks and 4 mono tracks. Then go to preferences/audio and set the import clips preference to mono.
AND:

Chris Tompkins
Video Atlanta LLC