Numark M2 connection issue (mixer > PC)

Hello music friends & co!

So, a buddy came over to my place and kindly gifted me a Numark M2 mixing table, a JVC hi-fi system (acting as an amp), and 4 speakers.
He did all the wiring; it was working perfectly! So I am set up in 4.1, all connected to my laptop. I had sound, and I could play with all the buttons on my table (treble, bass, mid, crossfader, etc.)

He must have taken some RCA cables, so I uninstalled my audio setup for a few days while I got some cables.
I bought all the missing cables and set up my system again:

- I connected the M2 table to my laptop via the green 3.5mm jack and in RCA on the RECORD of my table. Everything is fine so far.
- I connected all my speakers to my hi-fi system, everything works perfectly; if I play a CD on it, all my speakers work!
- I connected my hi-fi system to my table with an RCA/RCA cable, with my hi-fi set to AUX

And here's where my problem starts, the sound comes from all 4 speakers, but the issue is that I can no longer play with all my favorite little buttons! Unfortunately, based on my connection, I can only adjust the volume with my "master" button..
So, I can't adjust any buttons; my two chains (the vertical button lines, plus volume control + crossfader) don't work..

I've searched well before posting this article, but I found nothing regarding my case.
My connection is correct according to the manual ( http://www.numark.com/images/product_downloads/m2_quickstart_guide_v1_0.pdf )

Knowing that my friend is away in the army, and his barracks are over 300 miles from my place, he can't come to "fix" all this..

So I'm counting on you to provide me with as much help as possible!

Thanks in advance!

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