reciever vs seperates


Can someone either explain to me or point out a link that analyzes the differences between recievers and seperates? Specifically I know that seperates consist of pre-amps, amps, dacs, surround sound processors; what do each of these do? And more importantly which is likely to improve the sound over a standard reciever?

For example, I have a denon 3803 and i've heard that they don't have good dacs. Can I add a dac into this configuration and would it make a significant difference in quality. Which seperate is likely to increase quality the most over a reciever? thanks
tz7
Ohh .. I missed you other question.

I'd like a bigger sound stage (more projection from the speakers) and ability to listen at lower levels and still feel the music.
http://www.audioasylum.com/forums/MUG/bbs.html
Might try here for lots of info on mmg speakers. Have read that position is critical and many users tilt the speaker down toward the listening position. They are very revealing of upstream components and bad recordings. Be sure you are using a good quality recording while experimenting with placement. Would really consider trying an external amp. May give just what you are looking for after proper placement. Do try the link. There are so many there with hands on experience with these speakers that you should be able to get some good info and probably some there are using the 3802.
hth
Steve