I'm just checking you are refering to "My Library" and not "Limewire library"

Go to any file you want to play in My Library .. right cick > open with > select sonic stage. I think you will get a prompt to ask if you want to use this to open all files of this type > say yes, and that should be sorted. I use Mac and Windows may not work exactly as I said, but it should be near enough.

I hope this helps.

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