My understanding from chat sessions with Adobe is that you get to install on two machines. I have a Desktop that is win 7 64bit 16 gig mem quad i5 running now with Elements 11 and I have a laptop which is a MacBook Pro late 2013 OS X 10.9.4 64bit 16gig mem quad i7. My question is why can I use both a Mac and a Win machine as my two machines with the Licenses. According to the chat session is that it is only Two PC's running Win or Two Mac's running OS X.... NOT one of each... this makes no sense !!!
Why don't you download the Mac version 11 and try installing it on your Mac using the same serial number you used for the Windows machine. You will be able to answer your question first hand as to whether or not you can have mixed platforms.
Just as a clarification, Elements and Lightroom are pretty much the only Adobe products that allow you to use the same license for different platforms. All of the rest you have to pick one or the other but not both. That changes when you get into the Creative Cloud, where you can mix systems for any of the products you subscribe to.