Do they sound heavenly and eeeh playing the same music? If so, then it's definitely something else. If you can find a correlation (demanding source material) then it's probably the amp.
Does my amp have enough juice to power my speakers?
Having just read a review in Stereophile of my Audio Physic Step Plus speakers (which I have to my utter dismay ,knocked over and dinged AAAgh!), the author states that his Shindo Haut-Briton Power amp (20wpc) couldn't drive the Step Plusses and states that nothing less than 35Wpc could drive them. My dilemma is that I have a Line Magnetic 216 IA rated at 22Wpc that sometimes sounds heavenly and on other days sounds eeh. Do I need an amp with more boost?