I agree with JD, I have the Mk I version of the HDLs and found it does a slight but noticable improvement in eliminating high frequency hash. The designer of my speakers and I even used a spectrum analyzer of some sort on the tweeter with the same white noise signal, both with and without the HDLs, and the frequency response curve was slightly better with them in the system. The subjective effect to me was with high frequency instruments, such as bells and chimes, the image was a little more focused. Personally, I think that they and likely the OS devices as well are overpriced for what they are and do, at least new, but then again, it didn't stop me from buying them, now did it?
