>> The answer had ... been given ... on Win32 api newsgroup
That's about as helpful as "the answer is on the internet". Spam indeed.

>> API that will just give me the name of the installed sound card(s)
I can help with that at least (non WMI version)
http://www.codeguru.com/forum/showthread.php?t=453421

For duplex detection, have you dug around the DirectX api's?
http://www.codeguru.com/forum/showthread.php?t=424415

gg