Comment 29 for bug 348353

coling suggested:

You shouldn't need to specify either card NVidia or card 0. Just use the argument passed in and pass it through to the slave. It's just about cooking up the right .asoundrc syntax. Something like (untested):
{{{
pcm.Filter_A52Encode {
    @args [ CARD ]
    @args.CARD {
        type integer
        default 0
    }
    type a52
    bitrate 448
    channels 6
    card $CARD
}

pcm.a52 {
    @args [ CARD ]
    @args.CARD {
        type integer
        default 0
    }
    type rate
    slave {
        pcm "Filter_A52Encode"
        card $CARD
        rate 48000
    }
}
}}}