Absolutely! It wouldn't be easy, and would need some adjustments for colorspace etc but this is a method I have seen discussed online before. The speaker part

Absolutely! It wouldn't be easy, and would need some adjustments for colorspace etc but this is a method I have seen discussed online before. The speaker part is much easier. At some point in almost all modern audio systems, there will be a PCM signal as part of the DAC step. Hook in here, pipe that signal to a computer's audio in / microphone port, and you've got a pretty clean audio stream.