Aftermarket Stereo Installation

I am wanting to install an aftermarket cd player in my 03 trailblazer because i have the low model radio in mine, and it is not XM capable. I think I found which one i want, but then someone told me that if you put an aftermarket radio in, some features like Keyless Entry and the Door chime can become inoperative.... Any input would be appreciated. I work at a Chevy/Cadillac dealership but i cant get a straight answer from any of the guys at the shop.

only the chime would be lost but that is a quick fix w/ this part

http://www.circuitcity.com/ssm/Metra-GM-Class-II-Data-Interface--GMRC01-/sem/rpsm/oid/78044/rpem/ccd/productDetail.do