(It isn't even clear what it means by AMD Athlon motherboards, AMD750, AMD751, AMD760 chipsets? or any chipset that supports an Athlon?)
I'm not sure why there's a different one(because both supposedly address an issue with AMD Athlon motherboards).
The page it points to is an older update utility and older firmware, but you should be able to use the old update utility and newer firmware.
It's possible the new firmware upgrade utility had a problem running on certain systems, but I've run it before on an AMD750 based motherboard(and I'm inclined to think that's what they actually mean by AMD Athlon based motherboards) without any problems.
The 72X drive is currently on a 440BX based motherboard, and the utility froze during update until I turned off DMA and then did the update.
What's stranger if you read the one that it links to for AMD Athlon based mothernoards and Intel 820 chipset motherboards, it sounds more like you can ONLY use that for the motherboards it was intended for, but the normal upgrade utility will work on all boards including the ones the the older utility is for.
My advice, if your firmware is older than both of them, try the 221 first.
If you are running the 221 already, then by all means try the 226.
Personally, if I wasn't running the 226 I wouldn't care what the Kenwood page says, they're not very clear about what or why there are two different update utilities, I would go ahead and upgrade to the 226 by whatever means I can(be it the standard update utility, or downloading the older one and just loading the newer 226 firmware instead of the 221 firmware.