Soul Note DACs

"Expandable to dual mono DAC

You can select between STEREO, MONO Lch, and MONO Rch modes on the D-2. In MONO mode, the ES9038PROs in the opposite channel are disabled, thus doubling the power margin and making channel separation practically infinite."

Interesting! 

Cue up the "I don't like ESS Dac" posters. 

Soul Note and Esoteric (on their top few models) are the only DACs I have seen which let users double up for dual mono. I compared my D-2 to just a single one in stereo mode, while not twice as good it feels appreciably better.