I have a similar problem. My device has 2 audio outputs. The default is HDMI (when used as a media player with kodi), and I have a set of speakers on a CMedia USB sound card. I want mycroft to output all sound via the CMedia USB soundcard, via pulseaudio.
I've listed my sound sinks:
$ pacmd list-sinks | egrep "index|name:"
* index: 1
And I have changed play_wav_cmdline to:
"play_wav_cmdline": "paplay -d alsa_output.usb-0d8c_C-Media_USB_Headphone_Set-00.analog-stereo %1",
and this plays fine.
Unfortunately, I haven't found a way to tell mpg123 to use a specific sink for output. I'm guessing I need to use a different player.
And, thinking about that - it seems mplayer works just fine. Install it with
sudo apt-get install mplayer
And change your configuration to something like:
"play_mp3_cmdline": "mplayer -ao pulse::alsa_output.usb-0d8c_C-Media_USB_Headphone_Set-00.analog-stereo %1",
It works for me!