think of a stereo as a car...
consider the SPL aspect of it to be brute horsepower, and the SQ is the styling, aesthetics, and overall appeal of the car.
you can have a complete junker withloads of power that absolutly hauls ***, or you can have a refined car suitable for daily driving that will appease your taste as well as others, or you can have an overdone showcar that isnt fast and if you take it on the streets you risk damaging something.
likewise you can either have balls out SPL, a good mix suitable for your taste, or something that is purely intended to reproduce sound as it is meant to be...
all of course is subjective to the listener, different strokes for different folks...