Comment 33 for bug 348353

I was mistaken. I confused sinks and profiles. With $CARD, withe A52 profile does appear in the Hardware tab in the Sound preferences, so a suitable .asoundrc is:

pcm.a52 {
   @args [CARD]
   @args.CARD {
       type string
   }
   type rate
   slave {
       pcm {
           type a52
           bitrate 448
           channels 6
           card $CARD
       }
       rate 48000 #required somehow, otherwise nothing happens in PulseAudio
   }
}