I've tried the ODAC and Vali paired the Q701 and to my ears it was comparable and competes with the D100. Very similar sounding, the ODAC/Vali and D100. The D100 edges out maybe by a slight bit with better dynamics with the fatter bottom end and more airy highs (treble sensitive people need not apply and should go the Vali route though).
So the fact that people say the Modi and Odac are neck to neck, my only conclusion would be the Optical transport as the reason why its not much of an improvement. Regardless of the pure digital signal, it still needs the soundcard to process the 1's and 0's. The optical output you used is from the soundcard or built-in to the motherboard right? And just to throw it out there... its been said that coaxial or a nice usb receiver is a better route than toslink. I'd say give their usb version a try..
Edited by Soundsgoodtome - 6/11/14 at 12:51am