Wow, good thing I asked for details! yes, as nigel says, the signal you are getting from a receiver is not +/-4.8v, and it's not analog... it's a digital signal with a variable pulse width that controls a servo. This is EXACTLY what ESC's are made for. R/C electric motors can draw tens to hundreds of amps, they need to be driven by big, hefty power transistors in the proper manner, and building your own ESC is completely outside the realm of reality for a beginner at electronics; even if you could build one, it would cost you more money than simply buying one.
Again, your "additive" amplifier idea would be even LESS realistic in this situation... if you were trying to add to the 4.8v from the receiver, all the current for the motor would have to come from both the battery pack with which you power the motor, AND the receiver battery pack, which would cause the small cells in the receiver pack to immediately explode, for certain.
With most ESC's, you plug in a main (large) battery to the ESC, the ESC has a wire which supplies power to your receiver (which no longer requires its own battery), and has another wire that plugs into the receiver in place of the throttle servo that would have been in your gas model, and then of course the motor is connected to the ESC.
FYI, it would be a REALLY good idea for you to search around regarding the existing technology of electric R/C vehicles. Had you searched that, you would have realized that electrics still use the same kind of receivers as gas models, and use ESC's, not custom homemade amplifiers to drive the motor... Furthermore, with the kinds of high power that an electric is going to be using, you are going to need to do enough research that you know how to properly wire it up, with connectors and wire that are suitable for that amount of current, so you don't go blowing anything up. So, I would suggest you start searching and reading!