I can speak for the Yamaha 2400... the only difference between the 2400 and 1400 was: a bit more power, some different ICs and capacitors, and the ability to rev the firmware. I didn't think the difference warranted the extra money, and went with the 1400. The power has never been an issue, since I haven't even got close to any sign of distortion driving the M60s.
The Yamaha turned out to be a great choice for me. Its interface is extremely ergonomic, and ease of use is pretty impressive. The auto setup feature was really fun to play with, but in the end – I couldn’t help but tweak many of the settings. But, it gives you a great starting point. The entire device is the quintessential mark of quality: solid at the touch, each knob has that "solid and smooth" feel, at 37 lbs. it's strong, good craftsmanship even down to the remote (not like the flimsy Denon remote I got with my DVD player... I love the 2200 though -- please don't misconstrue, that puppy rocks!).
I read a lot of great things about the Denon amp, but in the end -- it came down to a "touchy feely" decision for me. And, the Yamaha had the right look and feel for me. Good luck with your decision, any of the 3 are going to make your mouth drop when you hear the axioms. It’s a very cool moment when you turn it on the first time, and listen to the first song.
