As Gordon Currie already pointed out the problem is not Windows Media Player but the WAV container, more specificly the format block stored in the WAV container.
Windows Media Player *does* support multi-channel, 24/32-bit WAV files out of the box, but the format block must use the WAVEFORMATEXTENSIBLE header. Why Microsoft decided to force this I'm not sure, I understand giving the option but it creates a lot of headaches by not supporting the legacy format.
That is why I wrote a DirectShow filter that gets inserted automatically when needed to translate from the WAVEFORMATEX format to the WAVEFORMATEXTENSIBLE format. Don't worry, not a single bit of data is changed in any way, what comes in is what goes out. Whether your sound card actually supports greater than 16-bits is a different issue but at least the files will play.
Get it here:
http://chrisnet.net/code.htm
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