The TF10 are great sounding IEM and am still using them everyday, so hopefully you can find my input helpful. Personally, I find the TF10 a little fatiguing on certain songs because of it’s treble and slightly lacking in bass punch, but overall I love how they sound.
I’ve listened and tried many of the headphones on your list when I was shopping around, so I think can provide some insight.
HFI-780: These are good headphones, but for me I found them to have too much bass. The bass is the star of these headphones and it’s very prominent and fills up the entirety of the headphones on every song. That’s not to say it’s not clear…they have good response on all frequencies but found the bass to perhaps veil the mids/highs and be a little loose. Compared to the TF10, I found the bass to be more powerful but not as detailed. The TF10 also have a more sparkly and engaging high, but the mids are about the same. Comfort wise, I found these to be a little to heavy for me with slight clamping force on my head. The pads and build are they isolate noise very well. These are perhaps better if you listen to more bass heavy music.
ATH-M50: These were my first foray into the world of better headphones and after many years, I have still kept these. Why? Because they sound very very good for the price and I find them to be perfect for taking them on the plane with me. These are very fun, warm headphones with good detail to all the frequencies. Compared to the TF10, these have more bass punch, but again it’s not as tightly controlled, though it doesn’t muddle the other sounds like the HFI-780 did. The mids and highs are crisp and fast but I found the TF10 to have slightly more detail and sparkle on the higher end. I would say these are more balanced than the HFI-780. Comfort wise, I love these…they aren’t as heavy as the HFI-780 and don’t have the clamping force while maintaining a good seal and isolation. The build quality is very good and I would recommend these for they are immensely versatile headphones, able to make all genres of music sound good.
SRH-840: Oh man do the trebles sound really good on these. They are really engaging and are the highlight of these headphones. They are just as good, if not better than the TF10 and it’s not fatiguing at all but very inviting, crisp and fast. The mids are clear and vocals come out very nicely with no shrill to them. However, I found them severely lacking in bass punch. The detail and separation is there, but it’s just not that prominent and this is such as shame because the mids/highs were gorgeous on these headphones. If you like the TF10, then I don’t think you’ll be fond of the lack of bass here. I think these headphones are good for rock and classical…that’s really about it, and more modern pop and hip-hop will just sound dry. Comfort wise, these are on the heavier/bulkier side but there’s no clamping force. Overall very comfortable with good isolation (though not as much as the HFI-780), but I personally prefer the M50 comfort.
AH-D2000: These are very good headphones with great detail on all frequencies. They tend to be bass monster, but I don’t think its as prominent and in your face as the HFI-780. It might be loose at times but and it’s not as tight as the TF10, but detail and depth is still there with more punch. The mids are just as detailed as the TF10, though again, sometimes I found myself missing the highs of the TF10. Overall the D2000 sound very fun and engaging, albeit very warm. One gripe I do have with these is the mid-bass hump which is prominent on all the songs and it bothered me a bit. However through some mods (though more expensive), I think you get rid of these to make it much better. Comfort wise, they are very good and are great looking headphones.
I haven’t listened to the other two, but from the above, I would recommend the M50 with the D2000 coming in a very close 2nd. If you don’t mind open headphones, then I would recommend the Ultrasone Pro2500 because I found them to be the very very close to the sound signature of the TF10 with slightly more bass punch. The highs and mids for these are just as good and detailed with a punchier and fast bass. Only downside I found is that the pads are a little shallow so after a couple hours of listening, the tip of my ears started to ache a bit.
You should take a look at some of the Sony closed headphones too. I found them to be very good and fun to listen to overall. Hope this helps.
