I just finished a shielded C7 cable for my Mac mini. I used a Furutech plug and C7. I had to do some major mods to the C7, which meant stripping it down completely. The cable is basically the same as yours though i just used three pieces of 16 gauge wire. One of the pieces was used solely as a "filler." I did not braid or twist the wire, but just laid it down straight, wrapped it in teflon tape, and then pulled the tinned copper sleeving over it. I soldered a ground to the tinned copper and grounded it to the AC plug just as you did.
The C7 was the tough part. The first one I got was defective and so they sent me a new one. I was going to use some PVC pipe, but instead used a cap from a bottle of guitar polish. After stripping off the C7 parts, taking a Dremel to it, and protecting the bare pieces with heat shrink; I put a little bit of hot glue on it to keep things from moving. I then put the "Dunlop" cap on, filled it with hot glue, and added the heat shrink. It made a considerable difference in the sound and I was able to do it for about 40% of the costs of a manufactured cable using the same components...minus the "Dunlop" cap.
The C7 Cable
(http://www.co-bw.com/Images_DIY_New/Fur_Cable.jpg)
The Hardware
(http://www.co-bw.com/Images_DIY_New/Fur_Cable_2.jpg)
Modified C7
(http://www.co-bw.com/Images_DIY_New/Fur_C7_Adapter.jpg)
Source of the Cap
(http://www.co-bw.com/Images_DIY_New/Fur_Dunlop_Bot.jpg)
The cap before cutting a hole in the top
(http://www.co-bw.com/Images_DIY_New/Fur_Dun_Cap.jpg)
