I've got a USB soundblaster Live card as the digital noise coming off the on-board sound was nothing short of awful. I can now play music with Amarok through the SB, but loads of surfing round the web doesn't seem to reveal how you do it for mplayer. I've seen suggestions of adding something along the lines of this to the command line:

-ao=alsa:device=External

But this just stops the program lanuching.

cat /proc/asound/cards

gives:

0 [ICH5 ]: ICH4 - Intel ICH5
Intel ICH5 with CMI9761 at 0xf7fff800, irq 20
1 [External ]: USB-Audio - SB Live! 24-bit External
Creative Technology SB Live! 24-bit External at usb-0000:00:1d.2-1, full speed

And, indeed, for Amarok, adding plughw:External makes it work just fine.

I'm guessing there's something you need to add to the driver config tab, but after trying a gazillion different things I'm stuck! Anyone able to help?