Faulty Multimedia system

I've got an Android multimedia system in my car, I think it is from the "Syncope" brand - from that box, it was pulled any way...
2 days ago, during driving, while listening to music, the speakers "yield" like a whistling sound for a couple of seconds and then all speakers became quiet beside one which started to sound like it's burnt.

This behavior repeating it-self each time I turn On the car...
The person who installed this Audio 3yrs ago, sais that the int. amp. got burnt...

Do you know if this issue can be fixed by hand? or should I replace this Audio?
Also, for the meantime, I would like to disconnect the Audio... can I just disconnect the speakers from the Audio system? or better to totally disconnect all cables from the stereo? - for the last one, should I disconnect the car battery before removing the power cable from the Audio? or no need for that?

* Due to the Coronavirus thing... it will take me some time to repair\replace this Audio... and this time I want to perform all needed actions my-self...

Thanks in advance!