I do something similar as my DAC needs to feed both my stereo and my headphone amp(s). The last two DAC's I've used were both balanced so they include RCA SE outputs and XLR balanced outputs. You could go the most basic route and use a splitter cable, this does reduce the overall voltage reaching either source. In my case I ran this setup on the XLR outputs, with the already higher voltage from the XLR splitting the signal didn't create issues on the downstream gear. Passive pre-amps will probably result in the least alteration of the signal. In the end getting a DAC with more outputs would be the best option, also the most the expensive. For three outputs you are looking at something like the Benchmark DAC 3 or Gungnir.