I have been fighting with my iMac 21'5 inch for the past couple of weeks and I think I've finally reached the final hurdle. I am able to successfully put windows 10 on my iMac via an efiboot, but the sound drivers refuse to work due to this. My conclusion is that I need a biosboot usb with the windows 10 iso file. For the life of me I cannot find anybody who has been able to tell me how to do this! Any and all help is greatly appreciated