I had the same observations when comparing both cans and bought the HD600's. I do the same, EQ up the bass to taste. I got better results, for myself, doing that than getting the HD650s as its treble is recessed compared to its mids. The HD600's are more sensitive and easier to amp.
Agreed. I'm really enjoying them and prefer them over the 650s but I can see why some people would own both. They certainly have different sound signatures. Not sure where the extra cost for the 650s comes from though. :)
It is bright, yes. Too bright? I don't think so. I only have about four hours of listening time on the combo so time will tell. However, I can say that the Schiit stack is similar to the Maverick Audio Tubemagic D1 Plus, albeit not as powerful (I think that DAC/Amp puts out twice the wattage at of the Magni at 300 ohms). Compared to a CMoy pocket amp, which can actually drive the 600s, the Schiit stack has much more clarity and "sparkle".