A home theater A/V Receiver and Amplifier assembly actually combines several different components. Some of which have a DVD or other media player built in. You can generally assemble a superior home theatre system by buying the components separately, but most people buy one unit that does all tasks because it’s more cost effective.
The Receiver’s components are:
Audio/video inputs for video sources (Blu-Ray, DVD player, DVR, PVR, etc.)
Pre-Amplifier, Surround-sound decoder (aka signal processor)
Power amplifiers for each sound channel, Outputs for speakers and television
The path of the audio and video is pretty straightforward. The source component (DVD player, DVR, etc.) feeds a signal to the receiver unit. You choose which input component you want to feed to your output unit, and the preamplifier selects this signal and amplifies its line level a little bit.
For more information about Amplifiers click here