you might want to query renault as to the make of the factory head unit.
there may be a chance the satellite stick & dash display will work with another model of the same make. otherwise, i dont like your chances.
personally, i think its just the speakers & no power amp that let the sound down. my rear speakers vibrate at moderate to high volumes - could just be theyve been mounted badly.
i would think a decent amp & beefier speakers would be enough to keep most audiophiles happy, unless you just HAVE to pull another part of the car out for the sake of sticking something different there - usually referred to as modding ;-P
joel.