Difference between ARC DAC7 and DAC8

Hi, I am planning to upgrade from Audio research DAC7 to DAC8 and want to know if there is significant differences between both these DACs. I am using squeezebox touch for now and going to use S/PDIF (Digital) connection . Need to switch to Music server later for to use USB.
Did you ever get an answer-- I'm looking at the 7 and 8 to purchase-thanks