I can only recommend the following page about this product: http://www.lautsprecher.org/bose-sound...
In the article you will find all the important information, such as the answer to your question:
"A stereo pairing function for connecting two SoundLink Minis together is not built in. This is a bit of a shame, but I think that very few users would really make use of such a function, after all, for the price of two SoundLink Minis you already get a decent stereo system."