How loud is too loud

Hi. Im new to the world of audiophile and am hoping someone can help with a problem only nine months in to spending £3000  on my set up. I've got an audiolab 8200p power amp, audiolab 8300cd and monitor audio silver 8 speakers. After playing some fairly heavy house music at -10db I noticed a distinct lack in sound quality when I played music at a lower volume and now it sounds as if I've lost a whole frequency level. There is not distortion as such, it's just that music sounds quieter and less definition in the top end. I always run my system in before turning up the volume and never push it too hard for too long. Normal listening level is around -30db.
Any suggestions greatly appreciated.