i bought the lifatec 8 years ago after i wrote this post - i can't say i really noticed a difference when i put it in from the cheap Kabeldirekt Optical. it sounds good, but i also have a short cheap coax cable on the same Node 2i -> DAC. The Coax sounds better.
better resolution was found by going from wifi to ethernet (powerline - gasp!) and putting a iFi audio LAN iSilencer on the back of the Node - huge improvement on solidity and reduction of jitter.
Cheers!