Here's what I did. First figure out which number the headset is:
$ cat /proc/asound/cards 0 [Headset ]: USB-Audio - Logitech USB Headset Logitech Logitech USB Headset at usb-0000:00:1d.1-1, full speed 1 [Intel ]: HDA-Intel - HDA Intel HDA Intel at 0xfebdc000 irq 16 2 [HDMI ]: HDA-Intel - HDA ATI HDMI HDA ATI HDMI at 0xfe9ec000 irq 17
Okay, so it's index 0. Then I made a new file called /etc/modprobe.d/sound and jammed this text in it:
options snd-usb-audio index=0
And then bingo bango bongo, there is sound in my Youtubes.