• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

building a high end DAC with tube outputs

Not clear what exactly is the aim. To build a heroic tubed i/v converter for a current output dac, or add a tube stage to a voltage output dac where it performs no particular technical function?

If the latter, why not just build a tube line stage? It will certainly offer more flexibility.