I recently also found that I have better control of the sound levels and more able to pinpoint where I want sound to be, if I turned my Windows volume levels. I currently have Windows volume at 45% and I find I'm much happier and have better audio control than when it was at 100% in Windows.
Basically instead of the 8AM-11AM on the dial only being usable, now I can use 8AM-5PM comfortably and with a lot of control in between
ps just wondering, what kind of computer do you have that you have optical connection in it? And FWIW I'm using USB on the Modi 3+, to my PC, and happy with it. Haven't noticed distortions or anything of the sort.