2002 trailblazer radio wiring

hey everyone,

                        got some good ??s...hoping to get some good answers :o)

i have a 2002 trailblazer just bought a alpine 7998 head unit... dont wanna cut any wires to my factory harness so i want to buy an aftemarket adapter. only problem is people are saying i need to keep my old radio still hooked up because of  the electronics..."scosche"    some people say i dont have that problem only the 2003s have that and i only need a regular adapter..."metra"  would rather buy scosche way better product and very easy to work with, but keep my factory radio under the seat still hooked up??? Technology is getting way out of hand!!! any help would be great.... also if anyone can get me some prices on install kits,  looking at the soundkase skgmt49-4 pretty sweet for a kit...thanks all....this site is the best