On the question of spatial qualities, this is *hugely* dependent on content. I have collected a library of content for headphone testing which shows this effect. Without it, it is easy to conclude that there is no such thing.
Also, frequency response in 1 to 3 kHz is a large determinant of this effect. Take any headphone you have and boost this region and listen for spatial qualities. Likely you hear the effect (ignore the tonality difference -- just listen for externalization of the sound).
As a Utopia owner, I just wanted to chime in on and add to the discussion with regards to soundstage. This isn't aimed at anyone in particular, and others including Amir may already know the of the following.
First, really appreciate the review and measurements on this headphone by ASR and members of its community (ie. SolderDude at DIYAudioHeaven).
Soundstage is one of those aspects that is greatly misunderstood in the headphone community. What is important to understand, is that the vast majority of music is designed for listening on stereo
speakers in a
room environment. When placing instruments in the stereo soundfield, an audio engineer can use a number of techniques including panning as well as spectral delay, eq and phase changes to make it appear that an instrument is positioned in space simulating both depth and imaging (stereo placement). When listening with speakers, your ears hear a blend of both channels, and this is required for these spatial cues to translate properly. In addition, you will also hear room reflections which impacts the presented frequency range and introduces transient delay, softening the sound and providing a degree of ambience.
In contrast, when listening to these same recordings on a headpphone, each stereo channel is heard discreetly, and without the natural room reflections. The resulting sound is that there is no effective 'center'. Instead, music can sound hard panned, like it is coming from directly left and right. You can adjust to this sound after a while but it simply incorrect. Many dedicated headphone listeners will also have acclimated to this sound, and spatial audio can take a bit to adjust to.
Crossfeed on its own cannot correct this. To hear proper soundstage on headphones would require you to listen to binaural recordings or stereo/multichannel content processed by spatial DSP. In both occasions, it would require that your headphones match a particular frequency curve and that your own individual HRTF (head related transfer function) is approximate to the DSP target model (or in the case of binaural recordings, the dummy head/ears used).
Now, headphones can sound spacious, but that is different than proper soundstage. Ive owned the HD800 in the past, and that headphone is very unique in that its frequency curve combined with the spectral delays introduced by its housing (speculating here) creates an effect somewhat similiar to a listening to a seashell. It was designed in a time before DSP was available outside of studio plugins. To a degree it created this effect, but at the expense of natural timbre.
The best I've heard for incredible soundstage and immersion is the Utopia using Waves Abbey Road Studio for stereo music, and Dolby Atmos for Headphones when processing multi-channel. Also, on its own the Utopia is incredible with most binaural recordings. Waves NX is freely available on iOS/Android but is no longer supported and has a clunky interface that resets parameters. It is still worth it, but it also is not as refined as the studio versions, as it introduces some peaks. With Abbey Road, you can choose from multiple speaker emulations and on the Utopia it is almost lifelike, like listening in a room to these speakers at different ranges. Interestingly, when I tested the same DSP with other headphones (ie. HD600), they cannot really render depth of field changes in speakers as well as the Utopia. I've set Abbey Road up on my Mac using a VST/Audio Unit host and bussing my audio through it. The program I use for this is Sound Source by Rogue Amoeba. I only use the stereo side of this on the Mac as bussing multichannel internally on the Mac is a huge pain. On Windows, the OS was designed with spatial audio in mind. It is simple to install the Netflix app and Dolby Atmos for Headphones to test. You need to use the app as Netflix through most browsers is only stereo.
There are other software that you can test this on. here is a a demo of
https://www.redscapeaudio.com/pages/preview (make sure to turn off any processing on your computer). YMMV depending on the tuning of your headphones and individual HRTF. Eventually, spatial DSP will be very common and easy to setup. A large driver of this being the gaming industry. Already there are some incredibly immersive games out there, and their spatial audio is typically built in. Also game audio is embracing object oriented positional audio instead of just surround sound on a single plane.
Lastly, in ear monitors can also do a great job with spatial audio. But this is another topic. I'll just say that the Etymotic IEM can be great with binaural content, but so can others (my recent BLON BL-05S being incredible especially for the price).