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
I've read through this thread and enjoy the opinions but something that hasn't been talked about is a bipolar stereo setup.I own definitive BP-8060-ST bipolar towers in a straight up stereo setup.I used a full 5.2 setup if you will for months and enjoyed it but having switched to stereo just using my towers I was even more impressed than my 5.2 setup.With my towers setup correctly I am getting an incredible 3D sound field...star wars episode 3 opening was the first movie I tested in stereo...and I was looking above and behind me as the ships flew around.These towers image very well and I have no need for a center or have a tough time with dialog.Music is just as impressive...I chose very well in my speaker choice.Happy listening...:)
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Multi-channel can be a gimmick to some but when I first used it I was impressed that it provided a very involving listening experience with movies. Fast forward a few years, my interest in it has diminished and I couldn't be bothered sometimes to play a movie using surround sound. Maybe because my first love and priority is two-channel. More recently I am gaining a little more interest in surround sound again and would like to revisit to see what I remember was so exciting.
It is the way we hear. Two channel make one sound with three dimension. I looked into SACD two channel was best; when more came out as multichannel, and I have found the best in NOT movie set-up, but two further out and wider ambient speakers.

You do not have part of orchestra playing in balcony, no. It is not like a movie where the car come from behind you.\

I very much like SACD, but stereo SACD is best.