What are Sonic differences DAC6e Mk 1, 2 ,3, 4?

What are the sonic differences between each update of the EMM Labs DAC6E?
There is no such thing as a MK1, 2, 3 and 4. There is a DAC6 and a DAC6e. The only differences are we added RCA connections and removed the fan which was for rack mounting.
Allow to me to re-state the question - The web site refers to the current DAC 6e as the fourth generation. What are the sonic differences?
The DAC6e that has been available to the public has always been the fourth generation of Ed Meitner's design. Earlier generations were only available to recording studios and have all been upgraded to the newest generation..