User blog comment:WonderfulAsia/Hetalia Sheet Music/@comment-74.102.9.179-20101201232838/@comment-2140341-20101202224251

Here is a link to the software that opens SDX files: http://www.kawai.co.jp/cmusic/download/spfx.htm

You'll need to unlock the software by entering a code, which you can attain by answering their survey. Software in Japanese, can use Google translate to help you.

If you have difficulties, contact me and I will help with you as best as possible!