I have just merged a set of changes from current to RELENG_4 for usb audio. USB audio in 4.x was not terribly well supported anyhow, but if you are running RELENG_4 and have a usb audio output device (input may not work, yet) you might like to do a "before and after" test. I have limited USB audio output equipment, and it didn't work on a lot of devices prior to these changes but I'd like to hear if it got worse :-)