Apple or Samsung USB-C dongles are fine, but on Android phones they require some fiddling in UAPP every time you connect them to get the volume limit removed.
You can do this for free (UAPP Trial works to unlock the volume), but it's a nuissance.

Also, the Samsung dongle is impedance-sensing, which means it slightly reduces maximum output voltage if you connect low impedance headphones, like K702 or the planars.

So I recommend something like Tempotec Sonata HD II, because it is using one of those ESS chips that have 2V output and do not care for headphone impedance.

You're welcome:-)

The reason such tiny our even immeasurable differences can work for us is psychological. Because the sound entering our ears is extremely complex, what our brain can do to reduce it to individual instruments, melody, sense of rhythm and even sense of sound quality is astonishing. We can't remember so much detail. When we expect a difference, we trick our minds to analyze the sound again and we can make new notions about the sound. Sound doesn't change (or changes very little), but we do.

Try to visualize how the palm of your hands looks like, for example. Then look at it and compare to what you imagined. The difference in the level of detail between our memory and the real- time emotive experience is crazy. If someone told you're developing some mild skin condition, how easy would it be for you to find something in that picture that is different to what you remember?

Off-topic, but try listening like that for a minute or two and then remove your hands. Now for a brief moment the music will sound a little off. Yet there are people who refuse to belive in brain adaptation as explanation for burn-in.

The format itself is quite flawed as it is 1-bit encoding with very high sampling rate.

The high sampling rate is required to apply noise shaping to move the noise outside of the audible band (over 20 kHz) and increase the signal-to-noise ration within the audible band.

DSD files have a lot of noise above 20 kHz. In best case you won't hear it.
In worst case, that noise can intermodulate with the audible frequencies, causing the noise to be added to the audible band, shifted in frequency and lowered in volume to the point it could cause some sensation of brightness.

That's theoretical.

You could convert the DSD file into high bitrate PCM (24/44.1 would remove the ultrasonic noise, 24/192 would keep some of it) and do a volume-matched double-blind test.

I've listened to a bunch of Grados and I consider Koss KSC75 the best take on such a sound flavour (in-your-face and airy). Everytime I listened to them they are better than I remember them.

You're in a tough spot, since MDR-7506 aren't bad headphones to begin with, at least based on measurements.

I haven't heard those, but it seems they have decent bass boost that doesn't bleed into the midrange, no excessive warmth, proper ear gain with maybe too much upper midrange and treble. It's all going to be "same, but different" from now on, especially if your friend already seems to have this attitude:)

I've had an occasion to listen to a Stax SR-007 (first version) and I wasn't blown away. I didn't hear all the detail or resolution I expected, based on what you can read online. Sure, they were sounding good, but that's it. No mind was blown. I'm more impressed by my Samsung Buds 2 since do seem to over-exaggerate detail (8 kHz boost) while still having a pleasant tonality overall. And I'm lucky to be one of the people who does experience soundstage in IEMs, at least with the music I listen to (soundstage is very dependent on the recording, though for may people IEMs will always sound closed-in).

I suppose if you really want to blow minds, for $200 you can get a pair of decent monitor speakers (JBL 305, Kali LP-6) and some good weed :) (if you don't have moral objections, legal issues with that in your country and no mental health risks like a history of schizophrenia or depression in your family, of course).

EDIT: Looks like a pair of JBL 305 is $300 and not $200.

I've never heard the HD660S, but bought a used HD700 with the intention of running them with Oratory1990's EQ setting, because of:

• low unit-to-unit variation
• low measurement variation depending on the placement on the head
• sound doesn't change that much with pad wear (reportedly HD6XX series pads change the sound after just a year).

That did not work with my K702, my unit had a different placement of peaks and dips in the FR. I settled on a bass shelf with them and was happy, though they do get fatiguing after a while.

With HD700 it worked well and the sound is very good. Has the non-fatiguing tonal balance of K371 but with more sparkle and soundstage.

Is that the MH1? I was a fan of MH1C, which was the version with the Apple pin layout.

In not sure if you can still get them. The MDR-EX15 are quite nice, though

Although I have AKG K702, I most often use Koss KSC75 for games, especially when virtual surround is engaged (Creative's SXFI or Sony's 3d Audio on PS5). There is just something about how they present spatial cues that I like at lot. And with SXFI's EQ they actually have bass.

Certainly worth a try I think and unlike most bigger headphones, they stick to your ears well and don't fall off - so are quite nice when doing house work and still wanting to hear your surroundings.

The Beyerdynamic DT770, DT880, DT990 are also well known for for their imaging capabilities. Have a listen if you can, maybe this presentation is what would work for you.

Also, for Sony's 3d Audio in supported games, I find AKG K371 doing surprisingly well. What I perceive in such circumstances is very good understanding of sound direction and sense of space. Great example of this are Returnal and Horizon Forbidden West. I guess the K371's accuracy help a lot. And their bass works well in games if you don't have any equalizer in your chain.