FWIW the current Voyetra sequencer "Record Producer"s help file says
SNG
This is the song file format used by Voyetra's Sequencer Plus series. Record Producer can read .SNG files, but it cannot save in this format.
Though I don't know if its true for Record Producer (a quick install reveals SNG
NOT in the open or import file dialogs but a drag&drop of a midi file renamed as .SNG works), it is true for its previous incarnation Digital Orchestrator Pro.
Rec Prod can run on Win98 & Win XP, DOP only works up to Win98.
HTH
edit to add : if Sen's offer doesn't work out let me know & we'll try DOP