We just got a 98 seville SLS with the factory 8 speaker stereo. Since then I have driven a 98 STS with the Bose stereo. If you go to EBAY I see you can get the BOSE head unit. How many pieces are involved in upgrading to the BOSE system? Besides the 8 speakers, what else is there?. Is it a plug and play system or is there some rewiring or additional cabling that would need to be done?