So I should keep the stock amp for the fronts and buy one for the rear? That would be the cheapest option? The only problem is that I want to keep everything stock except the speakers (adding an amp and wires is fine too) but I don't want to modify the basket or plastic trims just in case technology changes one day. I want future proof.

2nd option could be to buy to one 2 channel amp of the front and another for the back?