that "3d" quality

[cuttooth]

I already searched the DUC.
I've been running my digi001 mixes by a top guy with a Mix+ system, and he thinks they're good, but "thin". I hear the same thing. It's not EQ, and it's not reverb or panning or any kind of separation issue, it's just "thin". It doesn't have that 3D quality about it.
I have top-drawer instruments, great mics, and I know how to use them. I don't EQ too much (if you mic it right, you shouldn't have to), and there is very little in the signal path that would take the life out of my mixes. Personally, I think I'm running into the glass ceiling of "need new converters".
My question is this: when do you know that you've gotten all you can out of the digi001? When do you know that it's time to move on to better converters?