I've have build one. It was a project that took nearly a decade. The collection of the parts was the most time consuming. Building and testing took me about a year. The first casing i used was difficult for debugging so i made a second one from pine.
I have a nice hifi set from LINN (Wakonda and two LK100 amp) but the sound of my Millet amp with the K1000 beats it by far.
Sorry I can't upload any pictures yet because i'm new on the forum.
I made a page with some photo's of my headphone amp for the AKG K1000 so you have a look. The first version of the amp was in a casing like the one Pete Millet build. A bad one for debugging. This one look more like the Bottlehead Crack.