1. What errors were showing up in Device Manager and or Event Viewer?
2. Open up System Information from the System Tools Folder, and on the Tools Menu run the Direct X Diagnostic tool, and see if this finds any errors.
3. Make sure you have the latest version of Direct X
4. Uninstall the Yamaha and Technics drivers, then load the Yamaha drivers in first, to see if it is now recognised, if not then there is no conflict with the Technics driver, if however it does work, then load in the Technics driver and see if the problem returns, this will identify whether there really is any conflicts between the 2 drivers.
Point to Note it may be the Technics driver that is the problem, as I believe this was written before Win XP SP2 was released.
The drivers for XP Home/Pro/Media centre are all the same; the only difference between them is the features offered.
Hope this helps.

Bill