the leads are specificly for the sound set up you've got in teh car
the different sorts all have different plug shapes on the ends where they go in to the back of the radio head unit, a little notch here and there and a few different leads etc
don't try to plug the worn gleads into the wrong place as it's just going to blow shit up if it makes the wrong connections

and no, there isn't really a way to get it to work with the aftermarket stuff

don't cut any wires when you remove the thing, the sierra amp leads are failry rare ebcause the granada ones are way too short to use in their place

you will find that there is a double power type loom in the back of the radio/cd player
un hok this and if you follow it back you will find that it plugs into just one plug for the power etc
you will also find another 2 leads, red/yellow/blue plug covers on the ends
these link the cd to the radio
and then the radio goes to the amp
you then have ANOTHER power lead for the amp and finally the plugs for the speakers
you can get an iso cable long enough to reach from the amp location back to the normal position of the head unit and use another iso block to power up whatever you want to keep in there

as for removal of the amp, it slides up/down/sideways over a set of clips and then pings out