Are there any DACs that can go low?

I never heard this one before. The linearity and bandwidth of a DAC should be easy to quantify by manufacturers as well as reviewers. As Foster 9 suggests, maybe it is an impedance mismatch, or something of that sort.

Or your turntable is adding that fullness.

Quite frankly, sounds like you're describing the difference between a good vinyl rig and a good digital rig, particularly when you talk of the mids and highs. Are you saying that the digital setup does not go deeper, or does not SOUND as deep? A digital rig that is flat in the bass may have deep bass extension but not sound like it because it does not have a slight emphasis in the upper bass (much like some small monitor speakers might have a bump in the mid-bass to make you think you're hearing more bass than the speaker is actually producing). An easy way to test your digital system would be a test CD with bass tones, like the Stereophile ones. My guess is that Drubin is right, your vinyl rig may be adding a bit of fullness--not a bad thing, I might add.

I thought the Playback had a nice bass emphasis reminiscent of my Project RPM10.1 10cc evolution arm and a Sumiko Blackbird with 2g VTF played through my Bel Canto Phono3.

MyTek 192 DSD dac
Alan