OK, then this next part is COMPLETELY up to you. It may just brick your device. [color=#FF0000]Navitotal cannot be held responsible.[/color]
You can delete the Sony .exe and copy/paste the iGO8 from your computer making sure that all the paths to the program are properly changed and renamed. Also add my suggestions to the iGO8 sys.txt.
OR
You might have to delete the Sony nav program entirely and replace it with the iGO8 download.
Do you have nav-u.mscr now on your device? You might need to change it to this:
RegWriteDword ("HKCU", "ControlPanel\Volume", "Mute", 5)
Kill ("SonyCalibMan.exe")
Close("SonyAppMan")
Copy("\Mounted Volume\Sony\nav-u\MortScript.exe","\Windows\MortScript.exe")
Copy("\Mounted Volume\Sony\nav-u\toolhelp.dll","\Windows\toolhelp.dll")
Copy("\Mounted Volume\Sony\nav-u\TestMode.exe","\Windows\TestMode.exe")
Copy("\Mounted Volume\Sony\nav-u\PowerOn.mscr","\Windows\PowerOn.mscr")
RunOnPowerOn ("\Windows\MortScript.exe","\Windows\PowerOn.mscr" )
RunWait("\Mounted Volume\Sony\nav-u\ToolDevice.exe","off 18")
RunWait("\Mounted Volume\Sony\nav-u\ToolDevice.exe","off 15")
RunWait("\Mounted Volume\Sony\nav-u\ToolDevice.exe","on Serial")
Run ("\Windows\TestMode.exe")
Sleep (50)
Kill ("TestMode.exe")
While (TRUE)
RunWait ("\Mounted Volume\igo8\igo8.exe")
PowerOff
EndWhile