i was also having audio issues with my y500 after doing a fresh install of win8.1 no drivers were missing in device manager but that was only because standard drivers were being used for audio i only noticed after i realised the volume on full was not as loud anymore and after googling around i found Dolby Home Theater v4! v7.2.8000.14 which i believe was available on the stock y500 before this fixed my issue and also some nice options of equalization setting within the app