It may be helpful to identify how audio content can get hidden by your playback system. I think there are 5 major ways this happens:
1) Limited frequency extension: the content was too low or too high for your system to reproduce it.
2) Dips in the frequency response of your system: The content occurred at frequencies that are diminished in your playback system, causing them to be masked by other simultaneous content.
3) Peaks in the frequency response of your system: The missed content was masked by other simultaneous content that was exaggerated by your system.
4) Distortion: The content was missed because it was masked by distortion products created by your system.
5) Reflections / Reverberation: The content was masked by reflections of prior content that arrived simultaneously.
This may not be an exhaustive list, but if it's close, then it becomes clear that a good pair of headphones with smooth and extended frequency response and low distortion is hard to beat as far as hearing everything in the mix. However, that's not the most enjoyable way to experience music for many people (myself included: I'd much rather listen to my speakers than my studio quality headphones). The next best system for hearing everything would be a loudspeaker system with smooth, extended frequency response, low distortion, and high directivity (to limit reflections). In my experience, such a system isn't engaging, and is perceived as inauthentic. In the real world, sonic experiences aren't limited to a small fraction of space with a 53% span. Even if all the sound sources are within that span, we inevitably hear reflections from outside that span, which gives us a sense of the space we are in. For the most enjoyable experience, sidewall reflections that are substantially wider than 53%, and are delayed in time are helpful. In contrast, I don't think that floor and ceiling reflections add anything meaningful, besides possibly reinforcing low frequencies more than high frequencies and thus tilting the power spectrum. For me, the best combination of engagement, clarity, and perceived authenticity comes from my own DIY multi-way line array speakers (paired with multiple subwoofers). I have the extension, the smooth frequency response, the freedom from distortion even at high playback levels, and the reduction of reflections from the floor, ceiling, and front-wall (due to on-wall placement).
I've hosted numerous listening sessions with other enthusiasts, and I often get comments that I must not appreciate any other speakers. I don't really see myself as an audio snob. I appreciate the improvement a budget speaker system provides over the speakers in a TV or a soundbar. My threshold for "good" is not super high. I think the Sony SS-CS5s sound good. I recently spent some time listening to a prior DIY design of mine that was more conventional (MTM with 6.5" woofers and 1" tweeter in a ported tower). They are great speakers (and won me a prize at a DIY speaker competition.. placing 2nd in the open category). But I wouldn't listen to them for hours on end like I do with my line arrays. They probably have 97% of the performance that the arrays have, but that last 3 percent makes the difference between something that's a great speaker, and something that's more of an acoustic recreation device (or acoustic simulator).
I remember when I first heard my speakers properly positioned. I was struck with the thought that if these sounded so amazing, and they were designed and built by a novice (who works in an industry that's only somewhat related), then there must be speakers out there that capture all the excitement of a live performance. A knowledgeable fellow gave me a subtle warning that I was in for disappointment in the high end speaker industry. I tried every room at the next Capital Audio Fest. I failed to find audio Nirvana. In fact, I failed to find anything better than what I made at home. I've been to a few more shows and auditioned some high end systems... I still haven't heard a match for what I made at home.
