In order to get ALSA to work with your Bose speakers (after you have properly configured ALSA):
The trick is to set a new default device for ALSA.
$ cat /proc/asound/cards
My sample result:
0 [Intel ]: HDA-Intel - HDA Intel HDA Intel at 0xfdff8000 irq 16 1 [Audio ]: USB-Audio - Bose USB Audio Bose Corporation Bose USB Audio at usb-0000:00:1d.2-2, full speed
Look at /usr/share/alsa/alsa.conf and the find parameters you need to edit.
# defaults defaults.ctl.card 0 defaults.pcm.card 0
Change the default number on both values to the number that corresponds with your card. In my case, this is 1.
Then, select the device in System > Preferences > Sound (for Gnome) and change Alsa mixer volume settings.