FMOD Ex has stopped development and its license was not as friendly. I contacted them to ask about the use of FMOD Ex (FMOD 4.4) and they requested that openFrameworks upgrade due to licensing issues. There is currently no way to obtain an actual license for FMOD Ex.
FMOD 5's new license allows use for free as long as the development budget is under $500k and licensing after that is fairly cheap when compared to the budget. FMOD Ex can not be licensed anymore and is only used by people who are current licensees.