After getting everything working on my laptop I decided to test it against my wife's desktop. This is where I ran into problems. Although sound played fine on my laptop - sound on my wife's desktop either was not played or was not played in 3D. Very odd.
After searching MSDN and these forums and trying various things I came across a solution. When creating the SecondaryBuffer for the sound if I explicitly set the "LocateInSoftware" flag to "true" 3D sound worked flawlessly!
According to an MSDN article http://msdn2.microsoft.com/en-us/library/bb280909.aspx, this forces sound mixing to be performed by software and not the sound card hardware.
So, apparently not all sound cards are created equal...
Until next time....