start the terminal. (~$ means your logged in as a normal user, don't type it...)
cd to the directory containing the BrainVoyager executable:
~$ cd /Applications/BrainVoyager\ QX\ 64/BrainVoyager\ QX.app/Contents/MacOS/
start BrainVoyager by typing
~$ ./BrainVoyager\ QX &
start a following instance by typing the same command as in 3.
If you're running BrainVoyagerQX on a network license, additional steps are needed, namely to copy the nethasp.ini file into the directory where the executable lives: