para listar todos os dispositivos de som disponíveis (no meu exemplo 0 - placa PCI, 2 - saída interna interna)
root@012-music:/home/ishayahu # sysctl dev.pcm
....
dev.pcm.2.bitperfect: 0
dev.pcm.2.buffersize: 65536
dev.pcm.2.rec.autosrc: 2
dev.pcm.2.rec.32bit: 20
dev.pcm.2.rec.vchanformat: s16le:2.0
dev.pcm.2.rec.vchanrate: 48000
dev.pcm.2.rec.vchanmode: fixed
dev.pcm.2.rec.vchans: 1
dev.pcm.2.play.32bit: 24
dev.pcm.2.play.vchanformat: s16le:2.0
dev.pcm.2.play.vchanrate: 48000
dev.pcm.2.play.vchanmode: fixed
dev.pcm.2.play.vchans: 1
dev.pcm.2.%parent: hdaa1
dev.pcm.2.%pnpinfo:
dev.pcm.2.%location: nid=20,24,26
dev.pcm.2.%driver: pcm
dev.pcm.2.%desc: Realtek ALC883 (Rear Analog)dev.pcm.0.bitperfect: 0
...
dev.pcm.0.buffersize: 16384
dev.pcm.0.rec.vchanformat: s16le:2.0
dev.pcm.0.rec.vchanrate: 48000
dev.pcm.0.rec.vchanmode: fixed
dev.pcm.0.rec.vchans: 1
dev.pcm.0.play.vchanformat: s16le:2.0
dev.pcm.0.play.vchanrate: 48000
dev.pcm.0.play.vchanmode: fixed
dev.pcm.0.play.vchans: 1
dev.pcm.0.%parent: pci4
dev.pcm.0.%pnpinfo: vendor=0x125d device=0x1969 subvendor=0x125d subdevice=0x8888 class=0x040100
dev.pcm.0.%location: pci0:4:1:0
dev.pcm.0.%driver: pcm
dev.pcm.0.%desc: ESS Solo-1E
para reproduzir arquivos diferentes em diferentes saídas:
mpg123 -a /dev/dsp0.0 dir/file.mp3
mpg123 -a /dev/dsp2.0 dir2/file.mp3