@mihalis I simply shared what I experienced, with that MSB DAC and that same module. Which MSB DAC did you own? I don’t see it under the System for your current gear. So for the ProISL / ProUSB module combo, was it the same you had? That’s what I had.
My subsequent attempt in technicality of the benefits of USB protocol in streaming (or lack thereof) was simply based on my limited technical knowledge. I don’t pretend to be fully able to explain everything I hear.
As for the MSB ProISL / ProISL implementation, yes, the main objective is to eliminate copper, therefore the electrical interference associated with it, by introducing fiber. But it’s not as simple as that. The first device, what they call ProUSB (the dongle that stays outside the DAC, on it’s own) converts USB to their proprietary ISL audio transmission via the fiber. Then the module that goes into the DAC, what they call the ProISL module, is the one that is directly connected to the DAC architecture. Basically copper USB cable to the ProUSB dongle input, then fiber optics cable from the ProUSB dongle output, to the ProISL module (attached to the DAC) input.
So it’s not as simple as fiber, and here you go, all problems solved magically. The conversion itself is perhaps just as important, as in theory can introduce other issues.
Further, many of the non-believers will tell you that any of that is not an issue at all, and any competent Topping China $50 DAC has all that built in, galvanical isolation and all, so totally unnecessary to go through fiber they will tell you. So here is that.