May I suggest that since the 2.1 is still working out the kinks (as you have unfortunately found out), consider using the default alarm clock on the x10. Since I still have 1.6 (Thank You AT&T), I can only assume the alarm clock app on the X10 (originally with 1.6) is an X10 specific app. So, if that is true, stick to what you know works and than work into apps for non-urgent issues (Test them in other words). Plus with the default alarm, you can use the sounds provided or use your music (Which is the option I use)......
Good Luck................