I just bought a used DR-6. There are several versions relating to input options (bal vs. unbal); check first before you buy if that's important. I won't comment on the sound, since I haven't used it enough yet, but the first thing I noticed when I opened it was part orientation. In addition to generally good workmanship, all of the parts were installed so the part numbers face up, so you can see them. This is typical of well-trained assemblers (it's a mil requirement)that I thought speaks well about Classe's quality standards. As far as I can tell, the external power supply option just moves a small circuit board from a corner of the main board to a separate chassis, but it adds about 30-50% to the cost.