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.
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And as it's free, you should be able to bundle it with your game.
Ah, so it's up to the Construct users. Okay.