Hello all,
All is in the title ! My Realtek HP sound driver is tested and OK... I don't know the interest of Audio setting ON/OFF into the Stick/throttle settings, but I assigned a reverse button to be sure to maintain it ON, but... the Pitts engine (and others also) is always silent.
Thank you in advance for your fertile suggestions... 
[COSED] All my tests had been carried out with different planes, but always departing from the same Californian airport... All I had to do was change the site and the engines sounds were working correctly again with all the planes I had tried... Only the god of computer can understand, no doubt...