Kontrol S3 MK3 problem with audio output.

Hello everyone! This is my first post and probably is a stupid thing but i want to confirm with you guys.

A week ago i just got my Kontrol S3 and im super happy with it, my problem come when i was going to use my new headphones to prepare the next song. I have the situation that i cant use the headphones or if they work there is no sound coming from the speakers.

I use a IMAC 27" and the speakers are a normal computer ones, they dont have RCA only mini jack, so when i use the Kontrol i have to put the output settings on "In-build core" (or something like that, im sorry, im not at home and i dont quite remember the option) well, what i mean is i dont use the Kontrol S3, i used the computer one. This might be the problem? My theory is that using the computer as sound output you cant have the master and the monitors in different channels so i just bought a new pair of speakers, nothing crazy (https://www.amazon.es/Hercules-XPS-...s+Hercules+XPS+2.0&qid=1628497261&sr=8-1&th=1)
But they have an RCA entrance so i can plug them directly to the Kontrol and do a proper set up. This might solve my problem? Or im confused as hell?

Thanks for your time! And sorry for my english level, im from Spain and i dont use it everyday.

Cheers!