ive replaced the front 4x6 speakers with some $20 precision audio they sound great but i have a stupid loud setup in the car so my 4x6's are hardly even heard.
my setup
Two MTX 12' 400w subs in bandpass box
MTX 425w AMP
Two SDAT 6.5 speakers mounted on front doors
Two SDAT 6x9 speakers mounted where the medical kit used to be
4 SDAT's powered by a 400w 4ch audiovox amp
SDAT mp3 head unit
this is how it is in my car