Yeah I agree with your points benkei. Pretty sure the only way you could "communicate" with another computer, would be if it was listening for a signal and knew how to decode it. So only between two already infected computers. But the thing is, if it's hacking the bios it might be able to somehow set those devices to listen even if you reinstall the OS. But yeah, don't see how it would be able to infect a computer using audio signals, and they would need some good transmitters and receivers.
Either way, it's freaking crazy, and very next level thinking.