Difference between car audio system and portable speaker

Im an absolute noob when it comes to audio systems. Ive heard terms like impedance matching and having separate grounds, but im unaware as how to apply these stuff, anyways here it goes:

I designed a circuit which would turn on LEDs with intensity of the music (music reactive LEDs). I tested this using a portable Chinese speaker and it worked amazing. This makes me think that the circuit design I used for this is not @ fault for what I'm about to mention, anyways the circuit is attached.



I take the 12V from the car battery. The J1 connector is where i hook up the audio connection(Left or Right and ground). Now as i need 2 AUX wires, one for this setup and the other for the audio system itself, i make use of an AUX splitter, pic attached.


The male part of this goes into my phone, two AUX cables are plugged into the female end, one going to the audio output, while the other goes to my circuit.

Now the problem: When i plug this whole setup in the car, and plug the AUX into the car stereo system (KENWOOD) the LEDs do not work the way they should, for example they do no catch the beat of the music. Or the LEDs would stay lit even if there is no music playing. However if i just take out the AUX from the car stereo system (KENWOOD) and plug it into a portable speaker(keeping the rest of the setup same), the LEDs work flawlessly.

Please help me on how to solve this issue. I am totally clueless on this. If you find the information incomplete, I'll be happy clarify. And feel free to suggest any improvements to the circuit in question.

 

Is your car common ground or floating ground? Balanced or single ended?

 

I checked the connection of the ground coming from the AUX input with the ground of the car(battery) using a digital multi meter. It did NOT show a short circuit, which might mean it has a floating ground ?

In addition, after some googling, I was still unable to be sure if my car has a single ended system or a balanced one.

If it helps, the unit installed is Kenwood KDC W3044 (https://kasc.kenwood.com/files/prod/1163/5/KDC-W3544W_W3044_W313(EN).pdf)

Please ask away any questions as required as it might help you in helping me

Regards