*goodness... aftermarket radio/stereo systems have their own lock trick that i might be familiar with.
care to elaborate? i.e. what brand and model is ur aftermarket? i may or may not be able to help depending on what ur DIY skill is. ALPINE uses spring locks, KENWOOD, SONY, JVC, and most other use internal spring locks that may or may not need special removal tools...
then the more complicated part of it all.. the access codes.