Alan, Chicken Systems make some great translator products. I converted .gig file format via one of their products specifically for converting .gig files into ESX files so that I could use them with Logic. But if you have what is essentially a CD’s worth of samples, as in, the kind of samples you might use for hip hop or something, then the samples as wav files might be fine staying as .wav, and doing it manually, like you found that you can do.
After I converted a bunch of .gig orchestral type of samples, I realized that the samples for orchestral VI’s available today are so much better than the .gig files I had, so I stopped using them. I’m not sure if a free app to help you do bulk name-changing would help, but “NameChanger” (for mac) is really lightweight, smart and I use it when I have to modify a bunch of file names.