I posted a thread earlier regarding replacing the speaker system in my Cruze while retaining the factory head unit. I spoke to the manager of the shop to further understand what issue I'm facing that is preventing me from installing new speakers, amp, and a sub. I will be posting the information he emailed me below. If anyone has information on this, or has replaced the sound system in a 2015 Cruze LTZ with the upgraded pioneer system please let me know!
"...So, having said that, here’s what the situation is; GM and other carmakers incorporate a system into their vehicles that ties the sound system and throttle together through the car’s computer, or BCM (body control module). The factory sound system is activated when throttling up (stepping on the gas); it does two things when you step on the gas. One, is it creates a low level sub bass output that makes the engine sound “louder”, like you have a bigger engine under the hood. The other reason is… it acts as a type of cancellation system that offsets the actual exhaust system (works on a different sound frequency), so all you really hear is the sound system playing what sounds like exhaust.
This is all done through the car’s computer via a computer CAN wire; when you step on the gas, you are in essence sending a signal to the computer, telling the car’s computer to increase throttle, making the car go. That signal is then sent to the throttle position sensor, which increases the amount of gas being sent through the fuel injection system, thus increasing speed. The car’s computer then sends a signal to the car’s radio, telling it to generate that low level sub bass note emulating the sound of a car revving up; based on how heavy you push the throttle, the output level of the sub bass being generated by the sound system will either increase or decrease.
Now… when an aftermarket sound system is installed (connected) to the factory radio, this sound is amplified relative to the amount of power the aftermarket amplifier puts out. For example, if the factory amplifier is putting out 50 watts of power and you add a 500 watt amplifier to the system, the sound will be amplified 10 times. When this happens, that low level bass note generated by the car’s computer becomes horrendously loud and unbearable. It’s for this reason that it’s virtually impossible to connect anything to the factory radio, unless that programming can be bypassed somehow.
To date, no one that we know of has been able to figure out how to bypass that computer signal. Everyone I’ve spoken with has told me that the only way to eliminate the noise is to change out the factory radio for an aftermarket radio, which at this time is unfortunately not an option for your car…"
Sent from my iPhone using Tapatalk
"...So, having said that, here’s what the situation is; GM and other carmakers incorporate a system into their vehicles that ties the sound system and throttle together through the car’s computer, or BCM (body control module). The factory sound system is activated when throttling up (stepping on the gas); it does two things when you step on the gas. One, is it creates a low level sub bass output that makes the engine sound “louder”, like you have a bigger engine under the hood. The other reason is… it acts as a type of cancellation system that offsets the actual exhaust system (works on a different sound frequency), so all you really hear is the sound system playing what sounds like exhaust.
This is all done through the car’s computer via a computer CAN wire; when you step on the gas, you are in essence sending a signal to the computer, telling the car’s computer to increase throttle, making the car go. That signal is then sent to the throttle position sensor, which increases the amount of gas being sent through the fuel injection system, thus increasing speed. The car’s computer then sends a signal to the car’s radio, telling it to generate that low level sub bass note emulating the sound of a car revving up; based on how heavy you push the throttle, the output level of the sub bass being generated by the sound system will either increase or decrease.
Now… when an aftermarket sound system is installed (connected) to the factory radio, this sound is amplified relative to the amount of power the aftermarket amplifier puts out. For example, if the factory amplifier is putting out 50 watts of power and you add a 500 watt amplifier to the system, the sound will be amplified 10 times. When this happens, that low level bass note generated by the car’s computer becomes horrendously loud and unbearable. It’s for this reason that it’s virtually impossible to connect anything to the factory radio, unless that programming can be bypassed somehow.
To date, no one that we know of has been able to figure out how to bypass that computer signal. Everyone I’ve spoken with has told me that the only way to eliminate the noise is to change out the factory radio for an aftermarket radio, which at this time is unfortunately not an option for your car…"
Sent from my iPhone using Tapatalk
Singing sounds lost in the bass that kind of dissipates everywhere, and there isn't much clarity in the music. Turning it louder makes it so I can hear the higher notes better, but it by no means makes it sound any clearer, and the rear ledge speakers sound like they can't handle it even when I turn the bass in the EQ down. 
I love bass, but not when it's this terrible lol. 
