I have an aftermarket Sony HU with 2 kenwood door speakers i took out of my old car and chucked the two 6x9s i had in the back of it as they got ruined. This time ive got a 400w Wharfendale sub and just wondering which amp to get. Would i be right in thinking id need a 4 channel amp to hook the two door speakers up to it aswell as my sub? And to get one with at least 400w or more to share to the sub aswell as two speakers?

Im a total beginner when it comes to anything like this so any help would be great!