Since you're limited to HTML5's APIs, I don't think you'll be able to do anything crazy like interact directly with a soundcard.
I searched and these examples of capturing HTML5 audio, you may be able to interface with one of these libraries or examples.
http://www.html5rocks.com/en/tutorials/ ... dia/intro/
http://stackoverflow.com/questions/1641 ... io-to-file
These should at least give you an idea of what kinda limitations there are. I haven't done any called to external JS code from within Construct2, but I'm sure you could find help to figure that out.
Thanks for that, it's quite funny cod I would have thought since you can use webcam interaction and stuff, it might be easily possible. Instead of capturing there sound card, is there a way of streaming the audio from the output of the game to a file?