get uaudio pcm/mixer device name using devd

Hi all,

Using devd, is it possible to pass through to an action the pcm/mixer
device name created when a usb audio device is attached?

My objective is to set the default sound device to a specific usb audio
device, which can't be hardcoded via sysctl 'hw.snd.default_unit' due to
device order switching with multiple usb audio devices.

I have a working configuration using the following devd.conf:

notify 100 {
        match   "system"        "USB";
        match   "subsystem"     "INTERFACE";
        match   "type"          "ATTACH";

        match   "vendor"        "0x040d";
        match   "product"       "0x340b";

        action "/etc/set_usb_audio.sh";
};

and in set_usb_audio.sh:

#!/bin/sh
# get our preferred mixer
cardnumber=$(mixer -a | grep -F 'snd_uaudio (play)' | grep -o '[[:digit:]]\+')

if [ -n "$cardnumber" ]; then
        logger set_usb_audio.sh: found usb audio playback on dsp$cardnumber
        # set default audio card
        mixer -d "$cardnumber" >/dev/null

        # unmute our FX-AUDIO dac
        mixer -f /dev/mixer"$cardnumber" pcm2=1 >/dev/null
fi

mixer -a doesn't print the usb product names for my devices, its output
is generic, like:

pcm12:mixer: <USB audio> at ? kld snd_uaudio (play)
...
pcm13:mixer: <USB audio> at ? kld snd_uaudio (rec)

which makes my current matching method broad, hence the question about
passing through the pcm/mixer device name variable from devd.

Thanks,

mazin