You are right about the audio port. While Microstudio is open, it leaves the audio port assigned to it after it plays the first time.
This performance has been changed in our next release (Monday 05/21/01?) so the audio port is freed after playing ends. Check the
http://www.mtu.com/basics/news.htm page on Monday for release of Microstudio V2.300. That is what you want.
Also, make sure you have clicked on the
Beep option whenever it is visible.