Well I don't have a Sy99 but I do have a SY77. You will not be able to change the extension name of these files to make them useful. The only thing I can do for you is load your files into my SY77 and then it can send the sequence data to my pc and be recorded as a sysex file. If you can deal with a sysex file then this will be useful to you. But other than having a SY99 this is your only hope. Let me know if I can help.