Just received my new Channel Islands VHP-2 headphone amp which is connected to my desktop Mac via an AQ Dragonfly. Now I'd like to upgrade the DAC to either a CiAudio VDA-2/VAC-1 or a Halide DAC HD. The VDA-2 would be connected with a Toslinl cable (Mac mini toslink from the computer's headphone port) and the DAC HD with USB. Any feeling on which would sound better. Headphones are BeyerDynamic DT-880 (600 ohm) and Sennheiser HD600.