Aftermarket Speakers/Head unit - Help

[Field Rat]

I am attempting to install some Infinity Speakers to replace the factory speakers. I have already replaced the head unit with an alpine and have the GMOS-04 interface for the onstar. The system sounds like crap using this configuration. I want to keep the onstar. I am looking to solder rca jacks to the input wires just prior to the factory amp. Then to go to the aftermarket amp and to new speakers. Has anyone done this successfully. Help needed.

[Motohead]

On my Ram with the 7 speaker Infinity system I had to bypass the factory amp. I don't know if its a similar set up but if so, then if you are bypassing the factory amp you have to run new speaker lines to your speakers, can't use the old ones. I also used RCA output modules that turned the speaker outputs into RCA outputs. From there run the RCA's into the amp, from the amp to the speakers, using new speaker lines.

[kodiakz]

Field rat, you actually need to catch the output wires from the oem amp and run those through a high to low level converter. Or, you could use an external speaker wired directly to the gmos for onstar audio and then wire your head unit and/or amp directly to the speakers and bypass the oem amp.