the audiophile hobby endeavors to reproduce the live event, or so I believe
Don't agree. The audiophile goal is to accurately reproduce whatever is embedded in the media. The recording engineer and producer may, or may not, try to reproduce the live event. Audiophiles can only reproduce what has been recorded.
There is no agreed upon standard for what to do with the rear (or side) channels with multi-channel audio. There are no technical reasons why any musical element couldn't be assigned to any individual channel. The decisions are aesthetic in nature. Some of the productions may appear to be natural, others not so. For a large body of popular music the distinction is irrelevant in that no single musical event ever really occurred.
I've noticed in many of the replies that people have assigned the channel choice decision-making to the recording engineer. While that is possible, the more likely person in charge is the producer. There are exceptions, but for the most part recording engineers are technicians more concerned with the correct positioning of mics and avoiding level overload. The artistic vision of the music's ultimate presentation as heard by the public is usually determined by the producer.
Regarding the original question -- for me it comes down to how much well recorded multi-channel music that I like is available. In order to match the quality of my existing 2 channel system I estimate it would take an additional $15k minimum investment in source components, processors, amps, speakers and cables. I extrapolate that to mean there has to be at least $15k in multi-channel music that I would also buy in the near future. Your system and your music collection should have some sense of balance, IMO. As pointed out by others that amount of music isn't available. So why even have a multi-channel music system?
