Would it be an idea to support flac, because it's free, open source and royalty-free?
(let Construct read and play flac-files)
"A digital audio recording (such as a CD track) encoded to FLAC can be decompressed into an identical copy of the audio data."
http://en.wikipedia.org/wiki/Free_Lossless_Audio_Codec
If you and your target audience install the codec, you can play it with "Play music" in XAudio2.
And as it's free, you should be able to bundle it with your game.
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Ah, so it's up to the Construct users. Okay.