Sorry for late remark here, but galvanic isolation is trivial. All you need to achieve it is a powered usb hub and they are a dime a dozen... It can not be a deal breaker since it is very simple to fix.
Aby details to this thought? You will be introducing more rogue energy to the dac by a powered hub I am sure. ON the other hand, usb galvanic isolators/insulators are commonly found on ebay, so maybe that would help?