I hear you, but it is odd that you hear a difference. The Modi uses asynchronous USB input [like just about all other recent USB DACs]. It is extremely difficult to come up with a reason why the USB cable should make any difference at all in that scenario, certainly on the data side.
The Modi uses the USB cable for power also, not directly, but with some isolation and four internal regulators. Maybe just maybe, the cable makes a difference on the power supply side.
And please realize that I am not disputing what you hear. It's just that USB DACs used to be a disaster until the switch to asynchronous input was made and ever since the USB cable has been on a very long leash so to speak.
I hear you grufti. I wish I could explain i, because I wan't to understand what the contributing factor is in me hearing the difference. I will probably try other USB cables to see what varying degrees there are. To me it is night and day and at current, I favor the Generic .5 meter USB cable. Although it may be more fatiguing it's much funner to listen to.
I have experienced the same type of improvement, generally, and the same sort of improvement when I went to battery over USB power for my USB/SPDIF DD converter. Its definately there. Not a game changer IMO.
To me the change was to the lesser extent of tube rolling. Now mind you I did swap back and forth a few times to make sure I was hearing what I was hearing. I just didn't expect that big of a change. That being said I would be happy with either cable
I would also like to add that with what I have had to work with in terms of cables the difference in the USB cable made as much of a difference as the improvement (subjective I know) in my interconnect cables.