I received one of Calloways spare HD3's yesterday and I will say this, it is the first power cable I have tried in my system that has ever made such a dramatic difference to my home theater system. To give some background, I have a very non-exotic system consisting of Goldenear Triton Two's with Supersat 50's completing my 7.1 setup. Receiver is an Anthem MRX700. All sourcing to my system comes via HDMI or SPDIF off my HTPC. Here are my impressions from listening after I had it running for 24hrs "settling" into my system (remember Calloway already used these so break-in should be non-existent at this point:
Sound stage is IMMENSE, full, and three dimensional but most notable of everything was that every possible source of sound in the recordings is more detailed and distict. As others have said, it's as if the HD3 removes the restrictions of cabling from your setup and makes them seem to have disappeared. Classical scores sound far more real than before. Symphonies of strings sound like a true symphony of strings instead of a clump of string sound (if that makes any sense). The only way I can try to describe it is that they reminded me that there truly is a multitude of musicians playing each instrument in the orchestra. Dynamics were also taken to a new height. I just sat there saying to myself "oh, so that is what the this was supposed to sound like" again and again as I played more and more tracks.
An interesting tidbit I would like to add that the speaker wire used will make or break much of the "magic" of this power cord. I am currently using Mogami 3104 (single wired and ends crossed) which I find extremely detailed and airy and they match very well with this pc however I tried some MIT AVT1's for kicks and they are so dark sounding in comparison that they absorb a lot of what these power cords do so well at revealing from sources.
My power cord experience is the following: Black Sand Violet 2, Black Sand Violet MKII, Mojo Audio Enigma, Mojo Audio XPC-7.
Now here is the added bonus which I did not expect. With the HD3 plugged to my HTPC, not only did I experience all of the above for sound but I also felt the same effect on my Pioneer Elite 9G Kuro Plasma. Sharper image, more texture and detail on everything and more "pop" to the picture. The only way to describe it is that there is finer detail to walls, floors, faces like never before. Everything is just more discernable. I also had to knock the brightness down a little which was strange.
Anyway, I just wanted to add my 2 cents since I know there is very little on the web regarding reviews for these power cords. I'm sure my credibility will be hard to swallow since I only just created an account on Audiogon last week to get in contact with Calloway to try to buy one of his cords after researching them for days. But, anyway, there it is. My review for what it's worth.