After several says trying different firmwares I can confirm the following;

With original bitmain LPM firmware + original bmminer, just changing the frequency inside advance panel and modifying through css the fan speed control to 100%, right now I have my two antminers s9, one 13.0TH s9 running to 675 = 14.237TH and 73C and the other s9 14.00TH running 750 = 15.931TH and 80C and almost no hw errors and 1600w psu. So I´m not experiencing anymore the heat problems.