I have not been able to get the back-to-back USBe Perfects to work at the hard drive. I was able to get the back-to-back to work at the Lumin end, however. Which seems strange...
To me, (at this point) I believe it sounds better with the USBe Perfect used at both ends of the cable.
BTW, adding a Synergistic tuning (purple) dot on the usb cable at the hard drive is also an improvement.
ozzy