Though TBH I am kind of shocked that there are quality variations (sometimes the sound comes out tinny, sometimes it crackles, etc). I would think that it would basically just be doing the exact same math and outputting the same waveforms, so I don't really get why it' varies at all.
Maybe it uses some sort of compression or heuristics based on the output, and I can tell Tone.js "Take your time and give me the highest quality version of this" (possibly I could even write this to a cache...)