Again, the voltage on the hot wire powering the DAC is NOT referenced to whatever voltage is on the neutral pin of the plug (what you are calling "cold"), it is referenced to EARTH GROUND. If you apply -220 V to the neutral pin of the DAC's plug, then the power supply voltage seen by that DAC will vary from -64 V to +376 V because both the 110 Vrms AC on the hot pin and the -220 V DC on the neutral pin are referenced to EARTH GROUND. In addition, you have the safety ground pin which is at EARTH GROUND and if you try to establish a 220 V difference between the DAC's neutral and the DAC's safety ground, you will likely, depending on the details of the circuitry in the DAC box, cause a high current fault condition.