There's also the Amigo Sampler VST plugin you can use in your DAW for that 8 bit type of sound. I've seen a few you tube videos in my recommended. I'm not affiliated in any way, just thought to mention it.
Adobe Audition (previously CoolEdit) also supports .iff format, but I don't think it can do batch conversion. You do have options to convert to other sample types and rates with dithering types etc, to squeeze out a bit more dynamic range at the cost of a little bit of extra noise.