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Great article! I would only suggest another tip, go to eBay or Aliexpress, and search for "Mega328 Transistor Tester", it's a dirt cheap and portable little device to identify and test all sorts of components! I use mine everyday (e.g. for transistors and mosfets, it's a lot faster using it than searching for the datasheet), it even measures esr of capacitors!
I've actually done that two years ago, and its still working flawlessly. Between the amp and the main board (where all the outputs are), there are some cables that carry the audio signal for each channel, a GND, and MUTE button, where I connected directly a line signal. Mine was a Lennox player. Try checking if your device is similar to this ;-)