This is fully tested with Fruity Loops and will probably work with the other major sequencing apps. I can't suggest where to get Voyetra Sequencer Plus Gold as the FTP site prompted me for a login I didn't have.
When installing Voyetra, set the compatibility to Win95, Memory to separate and AUTO then run.
Don't select any drivers because it won't understand any of the new ones.
Got to DOS and launch the program from where you installed it. (C:\voyetra\spg.exe)
Watch it start and run as normal.
In order to CONVERT, open the original SNG file then change the MODE to MID.
Now you can save and it will save as a MIDI file.
Hope that helps guys! GL