I have successfully installed the XXHK3 firmware on my Samsung Galaxy S2. This firmware was release in August 2011. If you are having problem getting it via Kies, you may want to get it from this website and do it yourself.
How to Install XXKH3 on Samsung Galaxy S 2 (II) i9100 | The Android Soul
You need the software, Odin3 Ver 1.83 and above to update the firmware.