Here are updated instructions I got for pairing 2 Mini's together:
"For pairing the M90 MINI boomboxes together, make sure the bluetooth is shut off from the main device to connect. Turn on both M90 MINI boomboxes at the same time, wait for the boot-up sound to finish. Press the power button quickly, on both of the M90 MINI boomboxes to have each make the "boop" sound. NOW turn on the bluetooth from the phone, and you should hear both devices pair together with the unique "sparkle sound". These two M90 MINIs will now automatically pair up, any time they are being used together. "
I found this was almost correct. I did get to hear the sparkle sound, but neither radio would play bluetooth from my phone and the phone wouldn't connect with either option on my bluetooth list.... I looked at the bottom of my bluetooth devices list on my phone and a 3rd Mini M90 option was at the bottom. I clicked that option and it finally worked! So if you have 2 mini's you are pairing together and 2 mini options on your bluetooth list, look for the 3rd one and that will be the 'paired' option.