Been a while, and I've gotten more headphones and modded a few.
1: Sony DR-Z5: An old beast from the late 1970's/early 80's. Designed for portable CD players, which were just developed at the time, and is thus very easy to drive. Two words: Holy crap. Extremely detailed and fast. Their decay is instantaneous; better than the DT1350's even, and their attack is comparable to that of a high-end Grado. Neutral and flat, with very deep bass extension. Very slightly lacking in impact, more stat-like. Excellent imaging, relatively deep soundstage but very little width. Treble is amazing, cymbals are there and gone almost instantaneously with no splash or distortion. Absolutely no sound leakage and great isolation. Somewhat finicky fit, but very comfortable. Built like a tank and looks quite handsome. Possibly the best portable headphone in existence. Absolutely unbelievable.
2: KOSS Pro/4AAAA "Quad-A": This is the name I have given my modded 4AAA. They have been completely rewired with OFC, have dual-sided detachable cables and have been converted to a vented open-back design. Very warm and lush with a very smooth frequency response. Euphonic and impactful. Well-detailed and controlled sound. Very wide and deep soundstage with great imaging. Speaker-like bass, very tactile. Absolutely perfect isolation but lots of sound leakage due to the open back. Decent comfort, but pads are old and hard. Will be replaced soon. Very heavy; huge and tank-like. Difficult to drive so usage is typically reserved for home use. Excels with trance, EBM, hardstyle, etc. Sees a lot of use.
3: Beyerdynamic DT1350: Somewhat neutral. Very tightly controlled, lots of detail. Very good low end. Somewhat hazy midrange; artificial sounding treble. Warm and euphonic out of sub-par equipment but neutral and ruthlessly revealing when used with a better source. Very DAC-dependent. Excellent decay, decent attack. Somewhat diffuse imaging, very small soundstage. Amazing isolation and build quality. Very comfortable and stable. Light yet tank-like design, almost entirely made of nextel-coated aluminum.
4: Pioneer SE-700: Extremely neutral and flat with somewhat rolled off bass and upper treble. Excellent imaging but absolutely no soundstage. Somewhat thin with moderate attack and decay. Becomes fuller and faster out of more powerful amplifiers. Build is good, with lots of aluminum integrated into the design. One of the most gorgeous headphones ever made. Fit is somewhat loose and finicky, and the thin pads are bad for comfort. Since it was designed for speaker taps, this headphone is harder to drive than the HiFiMAN HE-6. The piezoelectric principle makes it unbelievably insensitive and its impedance is infinite. Aren't used very much due to this.
5: Pioneer SE-500: Similar to the SE-700 but even less bass due to the thinner diaphragm. Bright. More detailed and significantly easier to power than the SE-700 (though the SE-700 might be better with proper equipment). Even though they're bass-less, they are very exciting to listen to. Not quite as flat as the SE-700. Excellent imaging, decent soundstage. Much more snug fit-wise than the SE-700 and more comfortable too. They're different, but they still see some use.
6: KOSS K/6x Plus "Digital Ready": These headphones are pretty bad. These were my first headphones. I got them from a garage sale when I was somewhere around 12. They are very bassy, and have good treble and decent mids. Good imaging, but lacking soundstage. The deal breaker on this is the infamous "tin-can" veiling so common in headphones from the 80's. They also do not seal properly on the head due to the fixed yoke design, and thus aren't very comfortable either. However, KOSS's build quality is wonderful. Extremely sturdy plastic, aluminum struts, metal baffle. Very light.
7: AKG K240 Studio: I do not like these headphones. They are moderately detailed with an incredibly warm and airy signature, and beautiful treble. However... they have absolutely no control of the diaphragm. The attack and decay are so slow that it is possible to physically see the driver moving, which is extremely bad. They have a small soundstage and decent imaging. Somewhat passive and lacking in impact. Extremely comfortable and light, built like a tank, and has a nice detachable cable. I really want to like this headphone but I just don't.
8: Audio-Technica ATH-M50: Had these for almost 3 years now, and I've grown tired of them. Their low end doesn't have good extension and the highs are shrill and piercing. The lower mids simply aren't there, giving it a very hollow, thin sound. Not very fast in either attack or decay, and not very detailed because of it. No soundstage, poor imaging. Comfort is decent, fit is very loose. Basically just an all-around "meh". Extremely overrated; not recommended as anything but a first headphone, and be prepared to sell it because you're gonna want something better after a while. I'm keeping mine because it was a gift.
9: Sony MDR-SA3000: I'm sorry, but these headphones are terrible. They try to fake being fast by being trebley and dry, when in fact they lag behind headphones like the DR-Z5 and my friend's RS2i quite considerably. The entire sound is crammed up into the high registers. They lack any form of body or impact; very thin and uninvolving. There are no lower mids or bass, it's basically like listening to a 2-way headphone that only has the tweeter. Not a particularly good tweeter either. Their presentation sounds very closed-in, everything comes from a single spot in front of you with very little width and depth. Put simply, they don't do anything right. Can't believe these headphones are rated so highly.
Cheers!