I have an older 24” iMac that has run every version of Windows I’ve installed on it since Windows 7. Unfortunately, the audio disappeared when I upgraded from Windows 8 to Windows 8.1. I didn’t mind much, but every now and then I’d go into Device Manager, and there were no errors or problems reported there.
After digging through old posts on the Apple support forum I found a suggestion; try installing the latest Realtek Audio drivers.
It worked for me, and I hope that this little off-topic note helps someone else out there.
The Pen and Touch Support are there because I’ve got an early Wacom Bamboo tablet attached to the machine.