From what I gather, the stock speakers on the NX2000 are 4x6 in the front and 6 1/2 for the back. My car has a custom mount for 6 1/2 in the front as well, so i have 6 1/2 front and back. But I have noticed that the sound from the rear speakers is terrible opposed to the front speakers. I even tried switching the front and rear speakers... There is no bass whatsoever... I guess the acoustics of where the rear speakers sit is terrible. Has anyone done anything to make the rear speakers sound better?