[PROBLEM] Issue with sound card that have multiple device

[beanxinh]

Hi,

I have install moode-r760 on a RPi3 and use it with the Asus Xonar U7 MKII. It have analog and spdif out which I want to use the spdif to output the sound to a Sony PHA3. On aplay -l the card appear like this

card 2: MKII [Xonar U7 MKII], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: MKII [Xonar U7 MKII], device 1: USB Audio [USB Audio #1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: MKII [Xonar U7 MKII], device 2: USB Audio [USB Audio #2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

The SPDIF port is on device 1. I tried to change the output in web GUI but they do not have the option to choose the device, only allow to change the card. I tried to looking for a solution and come up with some post mentioned that changing /etc/alsa/conf.d/_audioout.conf will allow to change the output device so I manually changed it to

pcm._audioout {
type copy
slave.pcm "plughw:2,1"
}

and

pcm._audioout {
type copy
slave.pcm "hw:2,1"
}

but MPD and spotify still output on the old device.
After a while i figured that by changing /www/inc/playerlib.php in the below place

sysCmd("sed -i '/slave.pcm/c\slave.pcm \"" . $output_mode . ':' . $cardnum . ",0\"' " . ALSA_PLUGIN_PATH . '/_audioout.conf');
sysCmd("sed -i '/a { channels 2 pcm/c\a { channels 2 pcm \"" . $output_mode . ':' . $cardnum . ",0\" }' " . ALSA_PLUGIN_PATH . '/_sndaloop.conf');

and swap ",0\" to ",1\" and then using the web GUI to change the sound card I can output the sound to the spdif port. and when I took a look at the _audioout.conf file it changed to the same value that I manually inputted before

pcm._audioout {
type copy
slave.pcm "plughw:2,1"
}

So my question is what happened? Why manually changed the /etc/alsa/conf.d/_audioout.conf did not changed the output of the sound card? And if possible please add the ability to choose the device to your wonderful program in some future release.
Thank.