I got the D18 in the mail today.
It's quite clear that the D1 is in a higher league than the D18 but that isn't something to be ashamed of. You may be asking why I got this if the D1 is better. The reason is that this way I can switch out the Concero (which I have been having usb issues and was getting annoying using a usb/spdif converter when the main draw is usb) in my main rig. I can have the D1, emotiva mini X amp for my HE6 rig while I can use this setup for the HD800.
It is quite obvious to me that the D18 is a smooth sounding dac. It does make this rig sound a bit more easy going than before without losing much detail.