Replacing stock amplifier

I have a 2006 Pontiac G6 GTP with the "premium" 8 speaker monsoon sound system. It has 6.5" woofer and 1" tweeter in both doors, and two 2-way 6x9 in the rear deck. The monsoon amplifier is in the trunk on the right. Not much information is available about it specifically.

My car was the victim of a service bulletin of a water leak through a body seam which leaks right onto the amplifier. The amplifier is fried and I need my music back. A new Monsoon amplifier is almost $700 and the 3 connectors that need to be replaced will be about another $150.

I decided to go aftermarket because I can get better for a similar price. At the moment I don't want to change the stock headunit because it has my DIC built in.

My question here is how exactly do I connect the new amplifier to the stock head unit. I've asked on the G6 specific sites and I keep getting told to use a LOC. I feel like this answer is incomplete.

My understanding is that a LOC, is used to tap into AMPLIFIED wire signals to add a second amplifier. I won't have those wires because the stock amplifier is dead.

The signal wires coming from the headunit going to the stock amp are not RCAs, but I would assume that they are low level input and I can simply just remove the stock connector and put on RCA connectors and plug that into the new amplifier. However, I read somewhere on the internet that with stock headunits even the signal coming from the stock head unit may be a high input signal.

Does anybody know if it is high or low? Or how can I test it?
I do have a DMM and am familiar with how to use it.

So using my iphone I played a constant 1Khz track through the headunit, and using a DMM on A/C I checked the voltage of the signal and it seems to be low level input like I expected. (Was just under 4V)

I figured the Monsoon system is probably a 200W system, therefore likely to be 25W x 8 channels. So using V= Root(P*R) I expected the voltages to be around 10 V with the volume at max.

I then also found a wiring diagram tonight that indicated it as "low level audio signal"

So could I just snip the ends off the GM connector and wire them to RCAs and plug them into the low end on an aftermarket amp?