correct... head unit is juz a player that plays CD... for normal ppl, they'll check the xxW rating and thats it..
but for real, each brand's cd player has its own characteristic... for eg. alpine has a high trebel character, eclipse has a clean/natural character n so as other brands.. so, this reli depends on the taste of the listener..
then, follow by the DAC (digital analogue converter).. 1 bit DAC n 24bit DAC.. they surely make a large difference..
if the cd player is good, the amplifier in the HU itself is good as well... such as my alpine 9815.. it performs well in my bro's myvi wif stock speakers.. a good HU will last u more than 5 yrs cz my dad's Alpine HU juz had its b'day last month and its 7yrs old edi...
so... the more u pay, the more u get.. durability and satisfaction is there..