m1330 Speaker Selection

I've tried to listen to audio both through an HDMI cable and through my ExpressCard sound card hooked up to 5.1 speakers. I know to do this I need to select "Set Default" in the Sound control panel dialog for either my HDMI audio or my external sound card, but when pressing "Set Default" nothing happens and the internal speakers remain as the default. I can right-click and click "Test" on the non-internal speakers to hear some sound through my external speakers, but I cannot play music or video through the speakers. Any ideas?

Here's a screen grab:

Thanks!