Personally, I've been fixating on the soundstage and the sonic image created. If the amp gives you a very natural, realistic sound with great placing of individual instruments in their appropriate places on the sonic "stage", such that you are fooled into thinking you're "there" in a live event, that's getting into high end.
Others may fixate on other aspects of sound reproduction and will have their own criteria. That's what makes this audiophile world such a jungle and rightly so. Its what keeps it exciting. If there were set definitions to everything, we'd eventually have all the answers. Who wants that?
