Comment 24 for bug 1315212

http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html

pcm.name {
        type asym # Asym PCM
        playback STR # Playback slave name
        # or
        playback { # Playback slave definition
                pcm STR # Slave PCM name
                # or
                pcm { } # Slave PCM definition
        }
        capture STR # Capture slave name
        # or
        capture { # Capture slave definition
                pcm STR # Slave PCM name
                # or
                pcm { } # Slave PCM definition
        }
}

pcm.NAME {
        type hooks # PCM with hooks
        slave STR # Slave name
        # or
        slave { # Slave definition
                pcm STR # Slave PCM name
                # or
                pcm { } # Slave PCM definition
        }
        hooks {
                ID STR # Hook name (see pcm_hook)
                # or
                ID { } # Hook definition (see pcm_hook)
        }
}

you need to put the current ca0106 iec958 slave pcm and hook into playback slave and create capture slave of asym plugin