My Apple TV is a great little device for movies and casual music listening. But over time it gives me a headache if I listen too long. It's called listener fatigue.
Listener fatigue is an easy measurement guide that those of you who don't consider yourselves as "golden ears" can use to your advantage.
Examples of listener fatigue you may be familiar with include FM radio, where much of the music is compressed. Constant sound pressure without dynamic changes can certainly cause fatigue to the listener.
But even audio equipment with dynamics can, over a period of time, cause you to want to turn down the volume. This is a classic symptom of less-than-high-end audio gear.
I see mention of it in the forums all the time: "sounded great at first, but the more I listened the less I liked it".
Properly designed high-end audio equipment, from speakers to electronics, should have the opposite effect on you: that of wanting more, not less.
Keep an eye out for this in your system. Bright and hard, thin in the midbass, edgy, compressed on peaks, all signs that can contribute to this poor performance.
Listening shouldn't be a chore.