I bought a Denon midi set since I didn't feel like looking at a big surface of HIFi anymore. I found out that the better midi-sets indeed take up less space at the front, but they grow equally in depth. So basically, the machine has the same dimensions as "normal" HIFI, having swapped the front to the side.
My bookshelves are 30 cm deep (standard). I came to the following solution. I pulled out two shelves and added two sides. The sides are "fake", they don't continue in the shelves.