I've got an '06 Civic hybrid, with Navigation, that desperately needs an upgrade. I want to keep the stock HU though. I have a pair of Diamond Audio S600's and an old Memphis 4x75 amp that I would like to install. I wouldn't mind installing a sub under the passenger seat...if that option exists. Trunk mounted would be OK, however I don't want give up much of the little trunk space I have. I keep hearing that the new civic has a built in amp, separate from the HU. I assume that this amp is not powerful, or clean enough to drive the S600's and produce good sound. What is necessary to swap the factory amp with the Memphis? Can I even keep my stock HU? Is installing just the new speakers a viable option?