Re: One thing which hasn't been mentioned re MP3 encoding
If you can actually mp3s to decode, you have a way to detect problems which it's much easier than listening intently. Set up (or find a high schooler who can still do hardware) a good opamp with the original signal going in the plus and the signal run through the coder and decoderb into the minus, then adjust the levels to get the best cancellation, I.e. the output volume of the signal should be nearly zero. (Feed the opamp output into your listening system, I forgot to say) obviously, anything still audible will be distortion, caused by the digital process.
The last time I tried this with an outboard PCM encoder and decoder system I was really badly surprised at how much grunge was audible, and more importantly how really irritating it was. Admittedly, however, that was 30 years ago. I'm sure that since then, manufacturers have learned to make things worse.
Lest you think I'm an old crank, let me introduce to to the Aphex Exciter; a recording too used to deliberately add irritating distortion to the music, to make it really pop out at you. (Yes that's where Aphex twin got the name) When solid state took over from tubes, everybody raved about the brilliant highs, until they were proved to be distortion. Exact same thing when CDs took over from vinyl. Just add some popping and fizzing whenever your recording hits a high frequency, and it sounds awesome. But you get fatigued quite quickly.