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
Without all the technical knowledge that alot of the posters convey, I listen like it's real world. When you go to a concert of any kind, the stage is in front of you and instruments and vocals are projected to your seated location. As much as I would like to be sitting in the middle of what ever group is performing (5.1-7.1 surround) there is not enough room for all of us to sit there. So 2 channel with great sound engineering for stage presence of instruments and vocals gives me the most realistic sound imaging to the original performance.
Mostly Hi end audio multi or otherwise suffers from Environmental effects.. Fact is if you can get a 2 speaker system to work well in a single room environment, chances are adding speakers to that space from 3 other different points and angles in a room can in fact make it worse to a degree.

As stated above it can be done, but gets a lot more complex, especially for standard stereo recordings going thru multi channel processors. Bottom line it all starts, and ends with the room layout and acoustics. Sometimes just can't be done easily, and 2 channel imaging is easier to acheive period.

Many can argue what they want, but its not really all about "2 Channel gear" has been around longer, or has better hardware development, and or recordings due to cost factors... Its about the room and final setup that will cause most issues in 2 channel or multi. In the end no doubt people will find consitentley that 2 channel can work out better, but thats not to say a very well done multi channel can't compete, but yes it will normally cost much more, especially the room its in!
Many systems can't handle movies that were encoded with multi-channel where we want only a 2-channel delivery. The systems can't minimize the background noise in favor of dialog. It is hard to hear the movie as we would like.

I own an Anthem D2 that can process these multi tracks for two channel when I want two channel. For instance at a Superbowl party.
I wonder if technology since '02 could have changed the answer to this question a bit. I always thought that 2 channel would be better for fidelity than multi. In general that does seem to be the case with my stuff and most of my music. I do on the other hand have lots of electronic (gasp MP3's) that frankly sound pretty bad in 2 channel mode. I have found that for the bad stuff it sounds WAY better on my system to run my receiver in Extended Stereo mode and fake it to 5.1 channels. Maybe someone can explain it to me but it really helps. I wind up switching between 2.0 and 5.1 regularly. Mind, I'm not sure if this was a typical option in 2002.