We are aware that an issue can occur when using Nucleus USB Soundcard in Live 9! on Mac OS Lion, Mountain Lion + Mavericks.
The issue manifests as the played back audio dropping out after a few seconds, and can cause Live to hang or crash. It can occur in al version of the Nucleus USB Soundcard driver.
A fix for this issue is in development and will be released in the next Nucleus USB Soundcard software update.