this is true, thanks for the help evryone i shall now go back to my side if the fence

there is an amp and the head unit does have rca jacks (had to look up rca jacks on google)

i read all the posts on this subject and it all sounds very technical but lets just say i have no electricary knowledge and am the proud owner of a 2004 s40 and in said car i whould like to replace the head unit with one i allready own (not volvo i'm afraid) but when its conected the sound only come...