Since Schiit announced development of a revolutionary new USB design back at RMAF, you might want to hold off on upgrading or replacing your Yddgrasil until it is incorporated into production. Mike Moffat and Jason Stoddard of Schiit go on at some length about it in this
video (starting at about the 24 minute mark), and claim it's the first USB implementation that they believe to exceed the sonic performance of SPDIF.