Interface for aftermarket HU in 02 Tahoe?

Hey all, I'm confused about which interface module I need in order to retain door chimes, audible alerts, etc when replacing the factory HU in my 2002 Tahoe. Some info: 2002 Tahoe LT Non-bose With Onstar I don't want to use any of the factory stereo. I have an aftermarket HU, amps, components and subs. I don't NEED to keep the Onstar functionality (it looked like some of them offered the Onstar plugin as an optional module?), but if it's built into the unit then so be it. Do all of the interfaces include a speaker to play the audible alerts, or can they actually play through my aftermarket speakers in the doors? Thanks for any advice.

metra offers 3 units for this purpose: GMRC-01 has a speaker built in for door chimes and keeps all factory functionality; GMRC-02 uses external speaker for door chimes; GMOS-04 adds OnStar functionality; you're looking at $80-100 for the non-OnStar pieces, about $150 for the OnStar compatible one. There are pieces from other companies (scosche, etc.) but I'm not familiar with them; maybe someone else is.Life moves pretty fast; if you don't stop and look around once in a while; you could miss it.