I have been using an iBasso D10 Cobra as a USB DAC and recently discovered my computer has an optical audio out and have heard that optical is almost always > USB. When hooked up this way I do notice it sounds "airy'er" with more separation around the instruments however I am having major volume fluctuation issues. When a song gets more complex or more instruments join in it seems the volume of each instrument drops as to keep the overall volume level the same. This is kind of hard to explain. For example, say a track starts with an acoustic guitar opening before the whole band kicks in at once. Normally the track gets louder when the band kicks in but now its like the all of the instruments are toned down so the track does NOT get louder. Its like a complete loss of dynamics. I have played with the resolution settings in the Realtek HD Audio manager to no avail.