There are many ways to improve the sound of the EE DAC. The Burson Buffer is not one of them. While it does give a bit more current to the signal, it also increases the gain by 6 db. The output of the EE DAC is already between 2.5 volts on the solid state output and 3 volts on the tube output. Any more and you could overload the input stage on your pre-amp.
I have worked on both the EE DAC and the Burson Buffer. The Buffer can improve the sound of certain units with low powered, op-amp outputs. It would do wonders for a iPod or a stock SqueezeBox.
The EE DAC can be made to sound much better without having to resort to adding more things in the signal path.