So what are you suggesting? Getting power filters, extra expensive cables etc but not listening to Hans who supports all that crap?
If it's all about the voice in your head, then get an Intona USB 2.0 Isolator (the small version will do). It is an industrial device that is used in industry, medicine and measurement technology.
If you don't hear a difference, you can return it for 30 days and be sure there's no problem.
Basically, USB is a very cheap (by any means) and dirty interface. It's all the more amazing that it works so well in the audio field.
At least I haven't found a direct interface (e.g. AES, i2s or i2s over LVDS) that had any sound advantage for me. And I've tried a few things, including various hacks that tap directly from i2s.
With modern DACs, USB is not a problem for two reasons:
- Most DACs do not use the power supply from the USB line, so there can be no interference in the device.
- This also applies to the processing of the digital signal. It is so good in most of today's DACs that additional devices do not bring any improvement.
With many (especially cheap) computers and notebooks, the USB cable is very "dirty" and still works perfectly. That will be better with the Raspberry.