Problem With USB Audio Playback

[Mongoose.wa]

I broke the headphone jack on my laptop last week and have been relying on a Turtle Beach USB sound card for headphone use. It works perfectly out of the box in Windows, but has problems in Ubuntu 8.04.

When I plug it in and set all sound playback to USB Audio under System > Preferences > Sound, I get sound out of the right channel of my headphones, but the left is silent. In Volume Control, the left volume slider is stuck at the bottom and the channels can't be locked. The volume of the right channel is fine.

I assume it's not a problem with the hardware. It works like a charm in WinXP.

How can I get the left channel to output sound?

[noerrorsfound]

I have the same issue when trying to use a USB headset. I can use alsamixer but the volume controls on the headset change it through the GNOME volume control which means I can't use them.