Is there that much room in an echo for 6 15's? I'm talking about available airspace for them to breath......you can probably get them mocked up to fit but even if you start from the back of the front seat back I don't see how you can have enough room for them to get the room they need. Not to mention that echo's gonna sit a bit lower to say the least. Honestly I'd either pick a different car or stay with 3 12's. Get some subs that can handle more power and some bigger amps to power em and roll that way.Also don't be one of those tards blasting it at every chance just to prove how bad ass you are or something.