There are actually a number of audio interfaces that use either a lightning port or 30-pin port to connect direct to the interface and pass audio in and out.
The one that I am looking at however is a guitar amp with a USB-B port (Laney IRT Studio). It appears that it would work with the USB-camera adaptor because the manual states:
"Also compatible with Mac & iPad 1-3 via camera USB adaptor, iPad 4 & iPad Mini via Lightning-USB camera adaptor cable"
It also says:
"To run into iPad or iPad mini connect via a Camera USB adaptor, PC/MAC connects via standard A-B USB cable, for use with the likes of Garage Band, Audacity, Pro Tools and similar. It should be noted that the audio output of an iPad or iPad mini is disengaged and returned via the USB."
Assuming that the unit will work as intended with a USB-camera cable, I'd like to know if I can achieve the same thing with the USB-B to USB-A adaptor, as this will save me buying the USB-camera cable.
I would imagine that the USB-B connection on the amp/interface won't require bus power since the amp needs to be plugged into the mains electricity to work but I could be wrong.