think it's an issue with how the game interfaces with the directx API. I got my surround working on my Asus Xonar DX on my older XP box by setting it to 2 speaker in Windows, but setting the Xonar control panel to Quad with the GX extensions running (emulates EAX). It shouldn't be working, but positional audio works this way.

Been a long time since I used a Creative card... not sure if when you change the settings in the SB control panel if it will synch up with Windows, or if the EAX extensions are still available there either. But it might be something you can look at tinkering with if they still work somewhat independently.