Sat front row at the symphony...

The orchestra is in a huge shell-shaped proscenium.  Some years ago, an array of glass reflectors were suspended at the very top of this shell to improve  the balance of sound for the audience and to help the musicians hear each other.  I can attest to its success.  I can't fully account for the acoustic science of it, but it does work.  Flutes, horns, triangle, whatever...you can hear it in the terrace.  And out in the front of the house on the main floor, where I normally sit, I can hear the woodwinds better than I could in the olden days (for me, that would be the 1970s and '80s.)

@bigtwin Wait til you get your Sound Labs!  You’ll be amazed at how real it sounds. 
 

All the great halls sound good. But they also have front-of-house sound guys who are reinforcing the orchestra. All those small condenser mics hanging over the orchestra? Those are getting used. It’s subtle. These guys are good, and their equipment is top notch.  Their job is for you not to notice. 
 

I’m fortunate to sub with a top 10 orchestra from time to time. Last time I did, I brought up Sonic Tools on my iPad. Sitting just under the conductor by the first violins and <ten feet from the percussion section, the highest SPL on stage was 80dB. It was an orchestral fanfare, not Mahler. But classical music SLOs is much lower than jazz/pop/rock. I try to take that into account when listening at home. 

what mics? You mean there are speakers? It's not pure acoustic?

We have the Escondido Center for Performing Arts that has 2 nice theaters, one of decent size, and one smaller.  Both have great seats across the board.  The past 2 years the San Diego Symphony has performed on a regular basis while their main venue was being renovated, and have enjoyed attending the shows about every few months.  They recently had a 8 member string show that was supposed to be in the small theater, but for some reason was moved to the stage of the larger theater with the audience facing out looking over the regular seating, and the performers facing us.  They started with a duet, then trio, then quartet, ending up with all 8.  This was all natural, no mikes or speakers.  It was incredible!  Yes, sometimes we hear people coughing, or talking, etc, but still enjoyable and a good reference point to how music should sound!  Glad you had a wonderful experience!

Petaluman,

You said, "It's not about the sound."  Half true.  The live experience combines sound and visuals.  But the next time you attend a live concert, close your eyes and listen honestly to the sound.  The sound is the main subject of this discussion thread.  Many people here have addressed the comparison between the live concert sound and the home audio sound.  Although live unamplified sound is more natural than that of any audio system, at a location far away from the performers  so much detail is lost compared to any decent audio system playing a relatively unprocessed recording.  As a performing violinist, I listen carefully to my colleagues performing, and as a listener I seek to hear as much detail as possible to appreciate the music. To appreciate full details and nuances, no live location far away can compete with a good audio system.  But front row center always beats any audio system for detail and naturalness.

At a recent concert I heard the Prelude to Act 1 of Lohengrin by Wagner.  From front row center, the sound of the front stage string section was superb.  But the cymbal crash from the back of the stage was AWFUL--muddy from excessive distance and too much reverberation.  It sounded like the tweeter was blown on a bad speaker.  Even an intact low-fi audio system is better for clarity than that mess.