Here's the full quote...
-in_wave v3.0 doesn't support riff-wav's (ie. mp3 with wav header) or any codecs not supported by libsndfile library (eg. dsp truespeech or aud) | old in_wave from 5.13 *
(preliminary fix available in 5.21, requires setting up manually - info)
If you need support for mp3-layered riff wav, or another codec not supported by libsndfile, then it would probably be easier to use in_wave.dll from 5.13 (as linked to above), but note that it doesn't support multi-user profile setups.
I personally prefer to use the in_dshow workaround method, but yeah, it does take a few extra seconds to set it up manually, heh.