@lordmelton - I agree with you but it seems the cable actually worked for two months and then when the OP decided to use his DAC’s internal volume control, the cable was not compatible with that set up for some reason. It is a used cable, it worked for two months, and it apparently works except in the case of using the internal VC with the OP’s DAC. I understand his calling Mad Scientist to discuss and try to troubleshoot the situation, and I appreciate that Mad Scentist offered a discount on another of their USB cable products but, beyond that, at some point you take risks in order to save money by buying used stuff.
From a technical standpoint, I fail to understand how a USB cable would work with a DAC when it is set to zero attenuation and then fail to work when the DAC’s internal attenuation is engaged. Hasn’t the data transfer already been made by the time attenuation is applied?