The access to this sound test is very tricky, I quote here ReyVGM :
Play the game and get a game over. When the game over tune plays (or right before it ends), hold S + C + D + T until the sound test appears. Use the directional keys to select and play the songs.
If you use an emulator, you can come in trouble with your PC keyboard as many PC keyboards can't accept more than 2 or 3 keys pressed at the same time.
For blueMSX users, there's a solution by using the Keyboard editor :
- go to the Keyboard Config sub-directory
- make a copy of the blueMSX Default.config file (security measure : what follows will modify the original file)
- go in the keyboard part of the Input Editor
- map the D key of the MSX to the 8 key on the numpad
- map the T key of the MSX to the 9 key on the numpad
- click on Ok to quit the Input Editor
- keep a copy of the modified blueMSX Default.config file on another location on your harddisk (for a future new use)
And the trick is now : When the game over tune plays (or right before it ends), hold S + C + 8 numpad + 9 numpad until the sound test appears.
Enjoy ! 
