cs22

I've had the S4 for 3 days and have many questions regarding the Bose stereo. I understand that I cannot just replace the head unit or speakers. Can I add a sub w/out replacing everything? Can I use another amp (alpine v-12 5 channel) to power the sub and speakers? I get conflicting info from the stereo shops so I thought I would ask folks who have been through this. I would appreciate any info or suggestions. thanks.