Newbie amp help......why?

Im confused about why an amp is needed. I am not a cranker by any means. I dont listen to my music loud at all. I really dont listen to rock much so why is an amp needed? I could understand if it was like when i was younger and wanted more bass or better treble in my car but that was only because i wanted to listen louder without distortion. I have a old pioneer elite 39tx reciever/pre amp. I have a nad c541 transport, with psb stratus gold speakers. please help me understand how this works. My stuff will already go way louder without distortion than i would ever want to listen to at that level. thanx alot Kevin