Why is 2 Channel better than multi-channel?


I hear that the music fidelity of a multi-channel AV Receiver/Integrated amp can never match the sounds produced by a 2 channel system. Can someone clearly explain why this is so?

I'm planning to upgrade my HT system to try and achieve the best of both worlds, I currently have a 3 channel amp driving my SL, SR, C and a 2 channel amp driving my L and R.
I have a Denon 3801 acting as my pre. Is there any Pre/Proc out there that can merge both worlds with out breaking my bank? Looking for recommendations on what my next logical steps should be? Thanks in advance.
springowl
It's pretty logical and simple: Before the digital technology all recording engineeres needed is enough space and recording speed to place every detail of the live music onto the tape. Thus, 2ch recorders benefit with channel separation and amount of information stored per one channel on the magnetic tape to the multi-channel recorders. Also most of the professional recorders are using thick tape for the same reason. Mono recorders/reproducers are able to get maximum possible information(that's why I love mono recorded music)
Even in today's digital technology it does make a sence to still produce 2ch recordings guess why?... the same reason. Better channel separation and more information(bits) can be fit onto one track. Digital signal is nothing else but high analogue freequency with the phase shifts that we call digital samples.
Gboren: I think you don't understand the *possibilities* of 5.1. I've heard gimmicky recordings that put me in the middle of a barbershop quartet, and they sounded, well, gimmicky. What good multichannel should do is recreate the reverberant energy of a concert space. What should come from your surround speakers isn't instruments, but the reflections from the walls of the concert hall or whatever. Done right, it should sound like you're sitting in the middle of the hall, not in the middle of the orchestra. But not every recording engineer is equally adept at doing that. (Note the vast understatement there.)
Bomarc:
Fair enough. I fully agree about the possibilities of multichannel. But it has always been my impression that audio engineers have been putting their energy into creating more realistic explosions. When these same Terminator junkies master a music concert, they tend to use the same sensibility: put the listener in the middle of it.

I would love to hear multichannel music that is properly mastered. But where is it? How many titles are out there? And given the increased cost of setting up a multichannel system, will there ever be enough demand for audiophile multichannel to drive a market?
What about from a signaling perspective? Is analog signals that much better than digital signals that have been processed then converted back to analog and piped thru multi-channel? Are we talking about significant signal changes that are audible to the ears? Aren't information on the CD coded in digital form in the first place?
Most of us have speakers in the front that cost 4 to 5 times the amount of the ones in the back.