Well, I got em! Boy, these cans sure are impressive. They (obviously) don't have the impact or presence of my home or car stereo, but they are extremely comfortable, and extremely clear sounding. Wendy and I are new hearing details in songs we have heard thousands of times. The difference between MP3's and CD's is now VERY obvious, and sometimes extremely annoying.
The amplifier was necessary for these headphones, because at 250 ohms they are much trickier to drive than standard headphones. They do have surprising output off of the iPod though, definitely not as clear as the amp at high volumes, but it can play at a level sufficient for normal listening.
The amplifier does what it should, it doesn't really change the sound from the source that much... it just makes it louder, and allows more clarity at higher volumes. If you are happy with the output from your portable player or computer, you might not be overly impressed with an amplifier. The claims I have been hearing from people about improved bass, etc. from amplifying seem to be mostly exaggerated.
For example, if I compare my low impedance ER-6i headphones with or without an amplifier (at the same volume), I barely notice a change in the frequency response. The amplifier does work much better with various iPod EQ settings however, due to the added headroom. Switching to the line out on my iPod dock does sound a bit better, and running from my computer via USB to the built in DAC is even better. Regardless, at $150, this amplifier was a steal, and I highly recommend it.
The crossfeed effect on the amplifier is very noticeable. For certain recordings, it does indeed work as advertised, by making a slightly more coherent soundstage on heavily produced tracks. That is, for songs which have a lot of stereo separation (especially panning effects), you get less of that "in each ear" image. Since it also feeds the signal partially to the other channel, it sounds more like a home stereo would.
These headphones definitely play bass, but based on all the reviews I was reading, I was expecting to have my head blown off with a bloated bottom end. As it turns out, this only applies to the older all-black DT770 Pro's. The response in the new version, to my ears, is actually very even, especially after breaking them in. When I first got the headphones, they were even lacking in bass, and the treble was a bit bright. After I broke them in by playing the radio at high volumes overnight, they now sound much more even toned, much like the reference monitors I have heard. I am satisfied with this however, because the bass levels I have come to expect in my car would definitely become annoying for the long listening periods I have with my headphones.
The midrange is definitely less prominent than the Sennheisers I am used to (HD280pro, PX200, HD201, etc), because they do a much better job at treble and bass. The effect of the velour earpads almost makes it sound like you are in an anechoic chamber. The isolation is extremely good!
My favorite thing about these headphones is how amazingly COMFORTABLE they are. This is the only pair of headphones that I have been able to wear with my glasses and big flappy ears, yet find completely enjoyable after numerous hours of listening.
It is obvious that Headphones also suffer from the law of diminishing returns, much like home and car stereos. Most people would be just as happy with a $100 pair of headphones like the Sennheiser 280 Pros or even $70 Grado SR60's, as they would be with this $400 setup. There are definitely noticeable differences however, and to me, they were well worth it in this case.
I am now very excited to see what else these cans are capable of, given different types of amplifiers and recordings.