[letitbeirie]

> what you have is even more obviously a circumvention device

The device itself is just an "audio enhancer" - it could just as easily be used to spruce up the sound on old vinyl (pre-vinyl even) as it could to defeat copyright law.

The real issue with using it as OP intends is it's wholly unnecessary: the value in tools like youtube-dl is being asynchronous - you get the audio file without listening to the entire song first. OP's suggestion involving a speaker and a microphone is intrinsically synchronous, and it's a lot more work for lower quality than e.g. using Audacity to record the lossless digital audio off your sound bus.