Sound quality, pure and simple, is how accurately the source material is reproduced. There is no subjectivism, opinion or personal preference here. Either the system accurately reproduces the source (good sound quality) or it doesn't (poor sound quality).
Now, whether or not you prefer how something sounds is totally different (and irrelevant to true sound quality). If you like 145db of bass with only 110db of highs and that is not how the source material is recorded, then that is NOT sound quality no matter how you look at it. That's your personal preference, however.
I, aswell as many others, have went over that several times on this forum.