adapter for avalanche?

Ok, here's the problem...adding an aftermarket DVD player and amplifiers to my 2004 Avalanche w/Bose, and keeping my chimes and Onstar.  Without adding a separate speaker under the dash.  I can't use the Metra OS-04, are there any options that allow me to do this?  Thanks.

use the right harness and keep your door chime. This will also give you   your accessory wire because there is no accessory in the harness. Scosche DCGM09 NOTE: If using the DCGM09 with a Bose Audio system, connect the RCA from your new radio to the RCA ends of the DCGM09. If using the DCGM09 with a non-Bose audio system, simply cut off the DCGM09's RCA connectors and splice the speaker wires from your new radio to the newly-created speaker wires of the DCGM09. Bose amplifiers require a low-level input for proper signal balance between a high power aftermarket radio and the low-level input of a Bose amplifier. Using the RCA inputs from your radio with a non-Bose audio system will result in poor and very quiet sound quality.

Thanks, but won't work.  The factory amp has no speakers connected to it.  Aftermarket amps and speakers all around.

also the dcgm09 does not work with onstar I believe the adapter you want is the metra os01 circuit city sells it if I remember correctly it integrates with the bose and the onstar and allows for hookup of aftermarket radio then all amps and such will be hooked to that2008 Scion xB

Pioneer AVIC-D3

RF 3Sixty.2 sound processor

Stock speakers (for now ;))

Ok, let's say I go with a small amplified speaker under the dash.  What's a good speaker to use, and where would I get it?  I'm thinking a small computer style speaker, modified to run on 12 volts?

Any little cell phone speaker or any little inexpensive speaker will work, go to Radio Shack, they have them. The speaker will hook up the the OnStar interface, it does not need to be an amplified speaker.