I can't find a button in the XG control panel that brings up something like that, but here is the info by going to "Driver Details" on its properties in the device manager.
File name / version / provider:
c:\windows\system32\drivers\drmk.sys / 5.1.2600.1106 (xpsp1.020828.1920) / Microsoft
c:\windows\system32\drivers\ks.sys / 5.3.0000000.900 built by: DirectX / Microsoft
c:\windows\system32\drivers\portcls.sys / 5.1.2600.1106 (xpsp1.020828.1920) / Microsoft
c:\windows\system32\drivers\stream.sys / 5.3.0000000.900 built by: DirectX / Microsoft
c:\windows\system32\drivers\sxgxgwdm.sys / 5.13.2600.4 / YAMAHA CORPORATION
c:\windows\system32\ksproxy.ax / 5.3.0000000.900 built by: DirectX / Microsoft
c:\windows\system32\ksuser.ax / 5.3.0000000.900 built by: DirectX / Microsoft
c:\windows\system32\sxgapi32.dll / 1, 0, 0, 1 / YAMAHA CORPORATION
c:\windows\system32\sxgbin41.tbl / Unknown / Unknown
c:\windows\system32\sxgmasys.tbl / Unknown / Unknown
c:\windows\system32\sxgwave4.tbl / Unknown / Unknown
c:\windows\system32\wdmaud.drv / 5.1.2600.0 (XPClient.010817-1148) / Microsoft
Driver version: 5.13.2600.38
Date: 5/28/2002
Provider: YAMAHA CORPORATION (they really do like all caps)
Here's its control panel (this is not the driver properties thing) :
Obviously, some of those are Microsoft's files that get tacked on to any WDM audio device, and the rest are Yamaha files (those unknown ones are Yamaha too). Some of them look kind of like your files.
The solution could be a simple case of the installer not knowing that and putting them in the System folder instead of System32, thus killing Win2k/XP functionality...which means that the synth may actually work if we move all the files into the System32 folder, or even "System32/Drivers". If this is the case, no patch is necessary, and we can all say "Doh!" at our collective oversight of this.
I doubt it... Windows 9x and Windows 2000/XP don't use the same kind of drivers, so I doubt you'll get it to work by just moving the files.
You might be able to replace the wave files in the working S-YXG50 with the wave files from the S-YXG70 or something, but since they sound so similar anyway, might as well just get the S-YXG50.