Topic: Use an USB audio DAC to play audio instead of internal speaker.

Dear Sir,
I am trying to use an USB audio DAC to play audio instead of internal speaker.

At first, I just plugged USB cable into my Chumby Classic and hoped it could switch
sound out to my USB audio device automatically. However, nothing changed.

Thus, I enabled sshd and checked if ALSA USB driver worked. The result showed
my USB audio device was being detected.

The next step was to play audio from terminal. I used btplay with --output=alsa:hw:1,0.
to test my USB audio device.  This was not work, so I killed btplayd and re-run it with
--output=alsa:hw:1,0.  After btplayd was re-run, btplay could play audio via my USB audio
device. The sound also outputted to my USB audio when I played it from the touch panel
after re-running btplayd. However, my Chumby rebooted automatically after it finished
playing from touch panel.

My questions are:
1. Is there any way to switch sound output to USB automatically? Or I have to re-write
    udev rules?
2. Is system reboot after playing audio to an USB audio normally? Is it possible that my
    parameters for btplayd were incorrect or I have to modify other settings to avoid
    system to reboot?

Due to English is not my native language, if you do not understand what I write, just
let me know.  Thanks for your help.

Best Regards,