Although I haven't installed the latest VBox, the choice between PIIX3 and PIIX4 sounds like the options for the IDE controller. Are you definitely looking at the System tab, and not the Storage tab?
AhhhHA!! Thanks for the extra detail. You are right! I switched it from ICH9 to PIIX4 as Chipset under the System tab and the sound works. I was even able to hear the startup sound, which is a good indication sound works but I tested it in AHI OK.
So far so good! I'll test more and report back. Thanks Neil