Don't know any application that provide USB/serial output of the audio data,
Well, there's an interesting idea. I hadn't thought about a USB "sound card". Such certainly exist -- for example a cheap USB gaming headphone. Of course, using one of those and tapping into the signal with a high-impedance input would be a bit of a challenge. Might want to crack the box, and find the signal in pin for the DAC, and measure that. Of course, then there's still the issue of knowing the sample rate and the bit depth. Or, tapping the pin for analog out. Probably either of those is a teeny-tiny SMD lead.
Microphone is easier/cheaper.