It just means you cannot make a Mavericks installer key from 10.6.8.
Just to clarify, what I am suggesting is not making a Mavs installer key, but just a Mavs recovery key. To do that you would need to get on a Mavs Mac and purchase Mavs from the App Store with your AppleID from that machine then stop the download of the OS.
Then after that use the
recovery assistant tool with a 1GB or larger USB key to make a recovery key. This key does not contain the OS. All this tool does is move the small 650MB recovery partition from the host Mac to the USB key. Then you can option key boot to that key on your Mac and use the utilities on the key to erase your drive and download and install Mavericks.