[openal] Use OpenAL to playback to specific channel

[John Lee]

I have a system that currently uses two Dolby 7.1 sound cards, each uses 
OpenAL/alsoft to play different stereo output to different sets of speakers.

Since I do not need all the output channels on both cards, I'm looking 
to remove one of the sound cards in the system.

I've proven the hardware supports it by modifying my ALSA configuration 
files and I am able to play a sound to only one set of speakers using 
aplay -D setA /tmp/sound.wav and an ALSA PCM and the same sound to only 
the other set of speakers using another PCM: aplay -D setB 
/tmp/sound.wav. setA and setB are defined in the asound.conf file.

The playback devices that are available when I query OpenAL/alsoft are:

ALSA Software on Xonar DX [Multichannel] (hw:0,0)
ALSA Software on Xonar DX [Digital] (hw:0,1)

I'd love to be able to create "virtual" OpenAL devices that map to 
specific ALSA PCMs. Is that possible?

I can specify an ALSA PCM in the alsoft.conf file (via the device = 
tag), but don't see anywhere else that maps alsoft and ALSA devices.

Thanks in advance,
John