I'm in the same boat. Both rear speakers in my GT are blown, and I never have the system past 50% volume, nor the bass turned up past half. Needless to say I'm on the hunt for some new rear 6x9 speakers. I looked into the trunk and don't think installation will be too bad, although soldering wires together while laying on my back will be interesting. One thing I didn't do was to check impedance while I was looking at how they were installed.
I didn't notice that they are 4 wire. Perhaps I can find a way to mount two wire speakers. I'm not a fan of the Monsoon system as my Infinity system in my older Dodge is much clearer overall and has bass that I can crank up to shake the door panel and rear view mirror without causing a loss of clarity.
'11 Ram SXT 4x4 quad cab - 5.7L V8; 128,200kms
'09 Malibu 2Lt 3.6L - 140,000kms purchased 1 March 2019
'06 Pontiac G6 GT - 3.5L V6; 162,000kms (rear ended 15 Feb 2019, and given totalled title by insurance)