Sorry if this is more than a year late, but it's better then never I guess,
[edit: I just listened to episode #50 today!]
I am currently playing with OpenWRT and some cheap routers and bought this thing:
http://www.ebay.ca/itm/USB-2-0-3D-AUDIO-SOUND-CARD-ADAPTER-VIRTUAL-7-1-ch-/251102972733?pt=US_Sound_Card_External&hash=item3a76e74b3dFrom the description it is a "USB 2.0 3D External 7.1-Channel Audio Sound Card Adapter 12Mbps Portable Mini " and sells for less then 2 bucks US, shipping included!
It may not be the best quality but works ok and has, not one, but two mute buttons, along with volume control!
Even if you don't use it's on-board, hyper-quality mono mic input (pfft!) or it's "Virtual 7.1channel Surround sound", it's pretty cheap for a driverless, USB volume control!