I was going to say the AKG 240s 55ohm set, not MKII, the original, err, updated 240s, since there have been so many great 240 models I was very let down by those until recently.
I picked up a Grace 901 headphone amp, since, coming from speaker audiohile land, I was using so many parts from my main stereo that I didn't put as much money into a headphone amp, though it wasn't bad, it wasn't great for a high end setup, it was a Presonus HP4. I also used the headphone out on my Mackie VLZ3, anyway, I got the same results a lot of people get, ok midrange, kindof sleepy HF, and a pit of mud (not the fun kind!) for bass.
The Grace has changed my view on almost every set I own that were not immediately designed for a DAP, as in, other than my modded Aurvana Lives!/Denon 1001ks, it would sometimes make things worse, as the headstage and good low volume performance I got from my DAP, or a little NOS DAC with a tubed pre output that could drive porta pros, or esp. my XB700s to a wonderdully complete, natural, warm sound over the entire spectrum, just with an adapter to hook them up to the pre-out. (it has a headphone amp similar in power to the Presonus, but it is SS, not using the tube section).
Anyway, headphones I already liked a lot, Beyers, Senns, ATs, just sounded magical, even my DT770s w/ 880/990 pads, sound so natural, or the edge removed from my k271s (before the mkII as well).
I have managed to even get the Shure 440s to work as a pretty accurate monitor that won't shred me ears. A good tubed DAC (MHDT), a good tubed source, and the ultimate clean power of the Grace= such a pleasurably smooth, pleasing, and in some cases, sweet sound. It sounds almost entirely analog, even a 320k LAME mp3.
The DT990s, 250 ohms, used, seller said basically never used, so they came in a flawless looking box, the earpads felt new, but a dark secret lurked within. These things had been around the block so many times, the drivers had so much hair stuck to the membranes, the slightest bass note would crackle and whiff, it was aweful, just plain aweful. I wanted to have a complete set, 770s-990s, but I am just going to have to enjoy the 770s and 880s, and the new earpads on those 770s. The seller wo't contact me back, I disputed it, so we will see what happens, but I spent hours and hours carefully removing the hair stuck to the drivers, as you may know, beyer drivers use a special membrane that is almost "sticky" so when you remove a hair, it is sometimes almost melted into the driver membrane and you have to be extra careful to not pull the center voice coil out of it's channel, and the tiny voice coil wires from the solder points are so small they can hardly be seen, but sever one and that driver is gone.
After putting them back together, one driver still sounded like the same crap, the other, though did sound good. I figure there is hair on the underside of the driver, because there are holes all around the edge for air to move in and out, and if hair could hit the driver membrane, it could go into those holes, so i just gave up, there is really no way to fix it, you can't just remove the driver membrane and voice coil to access the underside!
I regret ever pressing that buy now button. I am sure he bought new earpads and put them on, along with the new foams that gome with them, called them new and hoped and idiot would buy them and not care.
Not fooling me pal, those things had to have been used for more than a few years, with many many hundreds of hours, ecept for the new pads. Even the driver housings, one had a stain on it, so some liquid made it through at one point, that explains the new foams too. I have a like new 990 pro box, a new set of 880/990 pads that sound great on my 770s, and headband/housing parts... I won't even say what I paid because it is too sad. I knew my 880s were probably better than the older 990 style, but i wanted to have a pair, because it is not always about "better", because I have several brands that bring equal pleasure, just in different moments and types of music, or environments.
I still want a pair of the older style 990s, but I am going to hold off on that one. The Grace can provide plenty of power to almost any headphone, so I can now actually consider a T1, or a much higher end AT model, even the warmth of the tubed parts of my chain could tame a set of k701s, or I could turn a pair of HD650s into a rocking set of cans, maybe set aside my sr350s and look into RS2, or RS1s. I am just enjoying the sets I have as most of them sound like new phones, such as the k240s that let so many people down, I am admiring how well it reproduces certain percussion instruments because the headphone can create a realistic decay, that "hollow" sound of sound reverberating out of a cylinder.