How do I make sure that the D1 DAC is set to 24-bit/96KHz audio?

If using a Mac, open the Audio MIDI Setup utility in Applications->Utilities, under Audio Devices, choose "Audioengine D1" and check that the format is set to 96 and the bit depth is set to 24bit. On a PC, open the sound options through the control panel. Then choose Speakers - Audioengine D1" and select Properties. You can select the output format from the dropdown in the advanced tab.