The OP brings up a very good point. Why do some types of music sound great on our systems and others, not so much?
I think one of the detriments of high end audio is that as one's system becomes more and more resolving, the ability to enjoy marginal recordings gets less and less. While one could debate that the Allman Bros recording referred to is good or not, it is certainly NOT a high resolution recording with ultra realistic sounding 'live un-amplified' instruments. Therefore, the better systems will typically pull out its flaws more. Same goes for a lot of rock recordings from the 70's. OTOH, there is a chain of thought that the very best speakers and gear will still portray these albums like the OP is hoping to hear them. This is somewhat true, IME, BUT it is still a factor that the better sounding recordings will still sound far more realistic than these older rock recordings. Depends on what one is listening for, because IF one is happy with the rock sound that I think the OP is striving for, then a large horn based system is the way to go...and the other aspects that he likes so much will become secondary. It really is horses for courses with a lot of this music...IMHO.