You don't really explain what you think it missing, but headphone listening cannot replicate certain aspects of stereo speaker listening. For instance:
- Headphones cannot create a solid soundstage which is in front of you the way speakers can. Headphone create great stereo separation, but it ranges from the sides of your head to the center of your head. Attempts to remedy this with crosstalk can sometimes help, but I feel it does more harm than good.
- The limitation on imaging to the space between your ears prevents headphones from providing the soundstage depth many can achieve with good speakers in a good room. The perception of performers being scattered on a stage in front of you, some closer and some farther away is difficult for headphone to accomplish.
- Headphones cannot create the impact and bodily vibration that good speakers (and/or subwoofer) can. They can generate tons of bass to well below 20Hz, but only your eardrums will sense that bass where a great home speaker system can shake your skin and bones.
- Headphones isolate the sound to your ears without room interaction, so any sense of ambience you are familiar with from your room's reverb and echoes won't be present in headphone listening. I consider this an advantage, but many folk who have learned to define high end sound by the way things sound in a room with all the room decay struggle with the only ambience you experience with headphones being in the source recording.
- Sense of scale is also a problem for headphones. I think a combination of everything I listed above contributes to a sense of size and scale that headphones simply cannot, nor never, will provide.
Those things are just the nature of headphone listening versus speaker listening. However, headphones offer benefits such as:
- Extremely low distortion
- Unlimited peak dynamic output which can exceed the capacity of your ears to handle
- Ultra-precise stereo imaging where you can define the location of the virtual sound source between your ears and in relation to the other sounds in the recording
- Extreme resolution and detail
- Surprisingly accurate midrange clarity
- Few, if any, speakers can provide those characteristics the way headphone can. Really, the experience is two different things. Headphones has benefits but also limitations, as do speakers in a room.
So, when you say something is missing, I struggle to understand what you mean since in certain aspect there are things missing which are impossible to accomplish through headphones. The same also goes for speakers which cannot do everything headphones can do easily.
Unfortunately, most online opinions and theories on headphone use are messed up and this notion that somehow spending more money and complicating a playback chain magically solves every problem are just wrong.
Nearly all of today's mobile phones, tablets, and notebook PCs have surprisingly good headphone and audio sections which do not need help in generating a very robust and accurate headphone output signal. Likewise, since about 2011 nearly all audio encoders perform better than our ears can hear (though data rate still matters). Pretty much any audio file with a data rate of over 192kbps, be it MP3, AAC, WMA, or whatever, will sound virtually identical to the original source. Some more complex recordings require a higher bit rate, but generally those are not the popular musical choices. High resolution audio is a snake oil gimmick 95% of the time, and the other 5% is rarely music anyone wants to listen to in the first place.
So, my struggle to understand your issue with headphones or IEMs limits my ability to help.
Keep in mind, getting higher resolution and clarity in the playback section can often be disappointing with the original music is not well recorded in the first place. No amount of upgrades will make Radiohead or Christina Aguilera sound like Steely Dan or any ECM jazz combo recording. This is an issue for many music fans who discover too late that their favorite songs sound just as good on a Kenwood stereo from the 1970s and it does on a state of the art $1M system from today. In those cases, just enjoying music knowing the playback cannot get any better is all you can hope for.
So, what is missing and what are you looking for?
