After my initial review of ATH-M50 vs. HFI-580 I was about 80% satisfied and having tasted what a good pair of headphones can do for my collection of music I wanted more. So I delved deeper in search of better sounding cans. My requirements stayed the same as before (closed-back, quality and strong bass, clear, crisp and forwarding mid/high, comfortable to wear for several hours) but this time I had some help with driving the cans, E7/E9 combo.
580 has about 120 hours, 770 has about 100 hours, and 900 has about 60 hours on them.
About E7 & E9
I’ve been listening on a Mac Pro (work computer) and when using a low ohm cans I can hear a constant hiss (very noticeable when not playing music). E7 completely removed it and played only the music, nothing else. That alone was enough to justify the cost for me as it really bothered me. On top of that, E7 can power all the cans in this review without any problems. There was, however, a limit to how loud it was able to drive. I was able to max out E7 on PRO 900 and wished if it could a little more (not that I would listen to music that loud all the time but I was hoping I was able to push it until my ears couldn’t take it, not the other way 
That’s where E9 stepped in. I’ve read the E9 was powerful enough to drive 600 ohm cans and I have no doubt. Also, as others mentioned E7/E9 combo didn’t add any colors to the sound they produced, very transparent, just louder and cleaner (when loud!).
Low Frequency
PRO 900 – This one has the most bass of all three. Definitely noticeable compared to 580 in quantity. It has strong bass all around (sub, mid and upper). 900 definitely kicks out the most bass-biased sound.
DT770 – Sub-bass is on par with PRO 900. Mid and upper bass is behind 900 and 580.Quantity is about the same as 900 in certain frequencies but the depth of bass feels shallower than 900 as well as punchness (due to weaker mid/upper bass, perhaps). For bassheads, this may be a bad thing but this could be good for people who prefer the bass to blend in better with the rest of the frequencies. Because of lack of mid/high bass (where you will feel that ‘kick’), it may sound a bit loose to some.
HFI-580 – Bass is tight but not as heavy as 900. Compared to 770, 580 does better with the mid/high bass but 770 projects deeper sub-bass better.
Mid Frequency
PRO 900 – I thought 580’s mid was clear as a blue sky but 900 ups it by one. It’s bright and clear. It sounds like there’s nothing standing in between a singer’s mouth and my ears. However, it sounds slightly recessed than 580. Again, I suspect a good part of this is due to bass- and treble-biased sound that is masking the mid.
HFI-580 – I quite like the mid on 580 as well. 580 has the most forwarding vocal of all three (it may feels slightly exaggerated even). When I compared it to M50 it was clear that 580 was the winner in clarity and brightness. When compared to 900 side by side, however, I was about to detect a very thin layer of muddiness over it. I wouldn't have been able to tell this apart if I didn't do immediate side-by-side comparison though. It's that minor.
DT770 – If 580 had a one thin layer of muddiness, this one has about 2. Not bad in all intents and purposes but against the two very good cans, it falls short a bit. Its mid feels a bit forward than 900 though. This could be due to the bass not eclipsing the mid/high as much as 900 which adds higher dose of bass to the music.
High
Pro 900 – Bright and clear separation of high frequency instruments such as cymbals and electric guitars is its strength. However, in certain songs with very high frequencies, it becomes a bit too bright and sibilant. I wish it was more like 580 when it comes to very high
HFI-580 - Yes, I love the high on 580! It's very clear, lively, and bright. I prefer 580 high frequency SQ over the other two as I sense no sibilance and it rolls off the very high freq just right whereas 900 plays all the way.
DT770 – This is 770’s weak point. There is not much of high when compared to the other two. Not much to see here, folks so move along.
Comfort
580 is, by far, the worst. Now, I wear glasses so this is a huge factor because pleather is inherently bad with glasses as there’s much less ‘give’ or conformation where the surface and the legs meet. Without glass, I can feel a little improvement but clamping force is still quite high compared to the other two (due to smaller contact patch as well). 770, hands down, is the most comfortable! I love wearing this! 770 has the largest pads of all so that helps as well. 900 is pretty good as well although the foam is a bit stiffer than 770’s.
The headband padding of 770 was the best as it provides all-around padding. I still have a bit of numbness on top of my head after wearing 770(better) and 580 for a couple of hours because of I have a pointy top 
may have to attach more padding on the sides to spread out the pressure.
Sound Stage
770 has the widest of all three and 580 has the narrowest. 900 is between the two. I can probably live with all three phones’ sound stages as this is not a top priority for me but there is noticeable in certain music.
Sound seal and leak
580’s strong clamping force with pleather pads provide the most sealing and least sound leak. Sound is barely heard when using these phones. 770 leaks the most. It’s at about 30% of my Grado SR80’s level. 900 falls in between but more towards 770.
Final Thoughts
There is no doubt that PRO 900 is bass biased. Considering this and the fact that I enjoy good bass (I don’t consider myself to be a basshead, however) I love how 900 puts every frequency together nicely to create one beautiful package. Sure there are parts that both 580 and 770 do better but when considering overall package, I prefer 900 over both. This also could mean that I favor the Ultrasone’s SQ and signature as I read that Ultrasone cans are either loved or hated.
Is 900 worth almost 3X the price of 580? I would say no as 900 will not give you 2.5x the performance of 580 considering that 580 is hell of value (dare I say more so than ATH-M50 
BUT there is no other headphones in that range that satisfy most (if not all) of my requirements like 900 does.
Also, I would choose 580 if I was on a tight budget. 900 will need an amp to reach its full potential so that will dissuade budget conscious listeners. 580 will not have much problem being driven by MP3 players and sound better. Also, 580 will render low quality music (128kbps) better than 900. 900 really deserves high quality source (FLAC, ALC) as it does very well with tight bottom end and high freq. that usually gets cut off by low bit rate music.
I tried to quantify and comment on each aspect of these headphones but in the end the true winner was the one that I couldn’t find any aspect that I feel I have to comment on.
PS. I purposely left out testing with classical music because frankly none of these phones excel with it. Perhaps 580 would be most suitable out of considering it’s more balanced approach. 900 is too bass-biased and 770 is not bright enough to impress anyone. I am sure there are many better, more natural sounding alternatives to these three phones for that genre.
