Apple - Restarting speakers without rebooting?

Try restarting the daemon process that processes audio by typing in Terminal:

sudo killall coreaudiod

This should reinitialize the audio and perhaps reload drivers.

Sometimes changing the sound output from your system preferences > sound panel will reinitialize the connection to your hardware. If you only have one output device available, try installing soundflower, just to have a second output in your list that you can cycle through.

Also: setting things back up after a reboot is a snap with snow leopard. It can remember which apps you had open and reopen them for you.

Try quitting CoreAudio from activity monitor, forcing it to relaunch itself.