Today I installed this gizmo from
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that provides stereo RCA connectors as a line-level auxilliary audio input to the Monsoon head unit.
This is on a 2000 Z28 Coupe with the UN0 option (Monsoon audio, single CD, 500W, 8 speakers).
The device is the PIE #GM9-AUX:
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which just plugs in-line to the 9-pin data port on the back of the head unit. Truely it was a 10-minute installation and now I can plug my iPod into the new auxillary input and it works great.
With the adapter installed, the head unit works as normal until you press the CD/Aux button when there is no CD inserted. Then it picks up the Aux input and whatever is connected to that plays through.