Sonnet Morpheus Owners! Preamp or Not?

Yes, thank you.  I'm in agreement on the Hermes/Morpheus being such a pleasure to listen to music through, and I too see no obvious upgrade path. In fact, I worry any change would be a change I wouldn't like - I'm super happy with this setup.

I like to have the precise volume and balance control, switching, etc of a preamp but don't want to sacrifice the quality of Morpheus in any way. If there was a bump upwards in sound with a preamp that would be a real plus.  I understand that while varying the voltage to the DAC boards is a clever volume option with little or no downside, wouldn't an optimum fixed voltage be best?

Thank you all for sharing your experiences please keep them coming.

The Pasithea DAC is a huge improvement over the Morpheus. Same sound profile, more space, detail, expanded frequency response. 
I’m using an Hermes into a Pasithea straight into a Metrum Forte. All designed by the same designer to work together without a preamp. 

Thanks, and then this preamp discussion should apply equally to the Pasithea as well as the Morpheus.