Further impressions:
* The Alpha Dog has really nice presentation of instrumental timbre and detail. The tuning accomplished by the structure of the new cups really helps to get a even, accurate presentation of the sound of instruments. The Mad Dog is also good at this - its lack of "ringing" gives it greater clarity than, say the HE-400 - but the lack of soundstage depth causes multiple instruments to interfere with each other (what is usually termed "congestion").
* Something about the new cup design of the Alpha Dog allows it to have significant soundstage depth, separating instruments away from each other, and making them individually identifiable. The combination of this with the excellent timbre, gives a very natural presentation of instruments not unlike some Magneplanar speakers.
* This makes the Alpha Dog really excellent with classical music. I listened to the amazing section of the RCA Living Stereo SACD of Scheherazade - "The Story of the Kalendar Prince" at 8:20-9:30 where Reiner gets a huge orchestra to turn on a dime like a jazz trio. The various instruments in the outstanding recording are spread out in front of you, left to right and front to back, and sound beautiful.
* In contrast, the accuracy of the Alpha Dog is not quite as compelling a factor with modern music like EDM. Such music has no real soundstage, and is so processed that it is impossible to tell what it is supposed to sound like - what is "correct". So, whatever produces the most enjoyable sound is best with modern music - regardless of accuracy. Amongst my headphones, the Mad Dog has the most enjoyable sound with EDM. The Mad Dog enhanced the exaggerated dynamics, harmonics and strong bass of Skrillex's "Rock 'n' Roll", while its midrange clarity made the effects all the more enjoyable. The more accurate and nuanced presentation of the Alpha Dog was no advantage with this track, especially since there is no soundstage depth of significance in the recording.
* So, if you listen to little or no jazz, blues, folk, bluegrass or classical at all, you will probably find the Mad Dog more to your liking. Its added warmth, slightly better dynamics, and better pairing with lesser equipment is ideal for 21st Century music styles. However if you listen to a good portion of those classic styles and also some modern music, then the Alpha Dog is an excellent choice, because its rendition of modern music is good enough to enjoy any piece of music. However, having both the Mad Dog and the Alpha Dog, I would find myself plugging in the Mad Dog to listen to EDM and even some reggae...