Its possible the amp just died of "natural causes" but from what i know (keep in mind this may not be 100% correct) The gmos 1 only concerves the chime, the rap, and onstar, it cant really modify the voltage. I work at best buy so i get to talk to the tech on that subject quite a bit. Even they wouldn't bother paying for the gmos 1 and unless someone asks for it or they have onstar, the head tech would rather just run it by using a standard harness adapter. This is because the gmos is designed to be used on multiple GM systems not just factory amplified ones. If the gmos could lower the voltage then it would affect every other car you installed it in as well. The one I have is just sitting in a box after I removed the stereo from my friends old Malibu, and trust me that thing didn't have an amp. This things not very substantial for a 100 dollar install piece tho.
If you want to bypass the amp you can pretty much just remove it and take off the clips from the amp then just put the color matching wires together. Keep in mind your sound will change drastically, tho probably for the better. Only real way to find out if the amp has failed is to check its input and output as well as the control wires and the power wires for it. You'll find those in their own clip next to the audio input and output clips if i remember right.
And yes if you didnt want to do the high line level outputs one of the solutions Ive seen on a few infinities was taking RCA cables and cutting them off and running the low level outputs into the amplifier but that would only work if your amp were going into protect mode (if it has a protect mode) or somthing of that sort. I guess its possible your gmos is having troubles as well. So this could be any number of wires or components. I'd break out the multimeter and get to checking.
