i have all the wires for cd change in trunk, no amp or cd changer.
i know the s-type and x-type changers are interchangable.
are the amps?

i found an 03 s-type amp for like 60$, wondering if it would hook up using the pre-existing wires in the trunk. also is the s-type amp an alpine as well?

 

The amps are the same for the X350 (XJ like mine) 2003-2009, X type (2004-) and S Type (after 2004 I think????) so an earlier S type one might not fit. Have a look at it and see if its a seperate amp with a power connector and d2b connector socket