I've Just edited this post because I found the answer, I feel sow stupid...
Solution:
Turns out I was renaming my downloaded file "kali-linux-1.0.4-armhf-n8000.img.xz" directly to "linux.img". I had to extract it first....
My bad, image works perfectly.
Problem:
I've followed all the steps as said in the guide.
When I'm booting in recovery modus, I receive the following messages:
mount: mount point /new_root/mnt/sdcard does not exist
fsck.ext2. Bad magic number in super-block while trying to open /dev/loop0
ERROR: fsck failed on 'dev/loop0'
ERROR: Failed to mount the real boot device
When I run e2fsck -y /storage/sdcard0/linux.img
I get: Superblock invalid, trying backup blocks...
Bad magic number in super-block while trying to open /storage/sdcard0/linux.img
efsck -b 8193 <device>
Anybody has a clue?
Thanks in advance