Heres how i setup my car ice:

Turn off all active/passive crossovers,bmx, and any form of sound modifiers in ur HU,pre-amp and amp..the point is to begin with true sound,no bass or treble.The sound should be totally flat.

Pop in your fav CD that you have heard a million times forward and backwards.Preferbly a song with good highs,mids and lows.By this i mean got bass,terble and midrange sounds.

Start with turning up the volume of head unit to 50% below what you normally listen to.
Turn up amp volume till volume is slightly higher than what you listen to.
Since my amp is powering my speakers and sub,i adjust the gains there till i like how the sound is.
After that,i adjust my HU settings till it sounds as superb as my setup can possibly get.
(my amp is better quality than my HU)

Sound is relative to the listener.You might not like my setup as i set it optimumly for heavy metal,but I like it.So the perfect,optimum setting is what you like to listen to.Some ppl prefer bassy sounds,I prefer more treble so i can hear the guitar solos clearly.

Have fun setting up ur system.And in the future you might want to add crossovers as they filter the sounds from your HU therefore better sound.