Hi went out and bought a Sony CD/MP3 headunit today but unsure if I can plug it straight in? Ive currently got the standard concert tape player (a3 1,8 se 1998). went to Halfords and got the spacers they told me I may need a PC9-401 to connect it at the rear of the unit. Later I went to another spares place and they told me I would be wasting my money getting one. Is this true? will it just plug in? what happens to the audi amp and sub? any help would be great!