Please describe the problem:
gnome-sound-properties does a great job of enumerating (and therefore enabling a user to select) the alsa hardware sound devices provided by a machine, but doesn't enumerate alsa software devices a user might specify in their .asoundrc.

namely, a user might specify a bluetooth audio device using bluez's support for it, but while they can't specify that as their default device within the .asoundrc, and then have gnome use the default device, it doesn't let them easily switch between them using gnome's interface.

Steps to reproduce:
1. add this entry to your .asoundrc

pcm.bluetooth {
   type bluetooth
   device 00:13:17:70:7E:F9
}

the device mac is for my a2dp headset

2. try to select it within gnome


Actual results:
it's not selectable

Expected results:
it to be enumerated a valid sound card

Does this happen every time?
yes

Other information: