Sound system without DSB

[Magid11]

Three months ago the stereo sound stopped coming from the passenger side, at the workshop they changed the amplifier box that exists in the back next to the buttery with a used one for 100 bucks. Now the sound stopped coming from the driver side and I want to change it myself.
1- Where can I buy this box? Links if possible
2- Is this box necessary or can I replace it with a plug or something simpler?
3- Anyone can recommend a good head unit that can replace that part? a head unit that does not require drowing cables all the way to the trunk.
Very thankful for any help or advise.