I was just looking at an owners manual online for a pioneer deck and it does say 22 watts rms but at 5% Total Harmonic Distortion. If you buy a decent amplifier they are usually rated at less than .1% Total Harmonic Distortion, and once you get into some high end amps they are less than .001% Total Harmonic Distortion. Decks dont put out much power and what they do put out is not very good.

 

The fact is, especially in an automobile, the amplifier (in your head unit or external)is the least of your worries. Speakers used for mids and highs commonly produce between 1% and 5% THD and for subwoofers the numbers can easily reach 10%. This doesn't even take into account all of the resonances of all of the plastic and metal panels in the vehicle.

Don't misunderstand what I said as meaning head units put out perfectly clean power, or sound better than external amps. The fact of the matter is that unless you get happy with the volume ****, any distortion present in your system you won't be able to hear anyway so the moral of the story is don't get carried away with the volume **** and push the deck harder than it's meant to be pushed.