I spent 2 days going through nsf's and youtube vids to find the right gradius game, and someone still beat me to it....dang.
http://www.youtube.com/watch?v=5St9izvlS44&feature=related
Honestly; vgthing actually wrote GR3EX in the module's title. That really wasn't guessing at all, if you ask me; that clue made it a bit too easy &, considering that vgthing is notorious for covering Gradius music, nicetas_c already had it right from the start.
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I never listened to much gradius music or played the games. I didn't really look to other clues (like the DPCM used) to help me. I didn't even listen to all the songs in the module, just the first one. I knew that it was a Konami game from the sounds so I approached it that way. I guess I made it harder on myself that way.