What if it is not the system and your ears? It could be that sometimes you could have higher than normal homocysteine levels and that makes the ears slightly full like a mild ear infection etc and can lead to sound that is less pleasing?
On another note do you ever notice it sounds better, more detail and louder late in the evening like near normal bed time? I seem to find the system is so much crisper and louder late at night and in darkness I prefer to listen most times since the eyes focus less and the ears and brain are more focused, kind of like closing your eyes for concentrated listening sessions etc..
