CM5908 gain adjustment? Hissing / static with new amp

[amarino]

Radio: CM5908 (rebuilt about 2 years ago with new capacitors)
Speakers: 4x Alpine S-S50
Amp: Kenwood KAC-M1824BT
Amp Manual: https://pdf.crutchfieldonline.com/Im...113M1824BT.PDF

The Amp claims to support Speaker Level Inputs with adapters to RCA plugs and the manual says:

"The output from the FACTORY INSTALLED HEAD UNIT up to 50W can be input. The power is turned on and off as the unit detects input signal (SIGNAL SENSING TURN-ON). Therefore it is not necessary to connect the power control wire."

I have a CM5908 Owners Manual and it says:

Power Amplifier
Power output (R=4 ohm, Vcc=13.8V)
10% THD 5.5W/CH
1% THD 4.5W/CH
THD (R=4 ohm, Vcc=13.8V)
Po=1W 0.1%
Frequency Response
(-3dB) 10 Hz to 60Hz
Signal/Noise Ratio 65 dB

When I have the amp in Bluetooth mode there is no hissing and the music sounds fine. When I switch to radio input there is background hissing/static and when using the volume knob of the radio it is super sensitive and the speakers quickly get way too loud just turning up the radio a tiny bit.

From everything I read it seems like I need Line Output Converters since I'm using speaker level inputs, but the Amp should be able to use speaker level inputs according to the manual.

I see there are some adjustment screws on the side of the CM5908 radio. Has anyone mapped these out to what they do? I'm hoping one of them is some sort of gain or volume adjustment?

[Vincenze]

You can use 2 resistors to lower the output level.
A variable resistor is even better for experiments. Connect one side to the ground, the other to the output signal, and take the lowered signal from the middle.

[amarino]

This cheap line output converter seemed to do the trick while bench testing tonight. I'll get everything back in the car tomorrow and see how it goes. https://www.crutchfield.com/p_249CSL...Converter.html

It still doesn't seem to trigger the amp auto-on via sensing the input side, so still need to run a seperate power switch.