I am not replacing the D1. When I get the WA6 I will be using the D1 as a DAC/pre-amp instead of a headphone amp.
The Woo Audio 3 is also a good choice for the dt880/600. Less expensive, too. Do a search on "dt880 wa3" and you'll find that it is a very popular combo, though many will say that dt880/600 like tube amps in general. But the WA3 and WA6 are popular choice. So are the Little Dot tube amps.
If you do get a tube amp to drive the dt880/600, which I would highly suggest doing, I'd recommend setting it out of reach of your daughter as the tubes do get hot.
Edited by Cal - 10/22/10 at 5:19pm