Hi, picked up my 54 180 quattro Coupe on Friday and have spent the last few days getting to know and enjoy her. What a fantastic car! Ive got a Bose Concert single slot CD fitted. Am I right in thinking it has the addition of an amp and should have plenty of quality sounds? The reason I ask is although it has plenty of clarity/volume it has no bass and sounds very "tinny". I only just discovered there are 2 speakers in the back (can't hear anything from them). Is this normal or is something amiss?