The Windows application
Goldwave comes with my highest recommendation, I've had the registered version for a few years now. Well worth the money. Especially when used for preparing and converting audio for use on "retro" platforms.
Anyway, it has excellent batch processing features and supports a wide variety of audio formats, not the least of which being WAV and IFF.
My only gripe is it's a little buggy when running from Linux/Wine, can't create a new waveform for some reason, but it can still load and save just fine.
I could probably name at least half a dozen WAV>IFF converters for Amiga which have yet to be named in this thread, but you did specify in the original post that PC software would be preferred, and I can totally understand why. So I won't bother.