I could be wrong, but I think you're going to have a tough time finding multidisk support for the Amiga. My A4000 system hard drive device is DH0 while my A1200 device is HD0. Some people name their boot drive "System" while others label it "Workbench". An unpacker wouldn't be able to find the right device half the time and would fail to extract the files, unless its unpacking on the system that created the archive. You could always relabel your drives temporarily, assuming the unzipper gives a decent error message telling you what device name it's looking for. The PC side is easier for multidisk support because drives are labeled C, D, etc.
Anyway, I use Un/ZipPPC on the Amiga. It's at least in the ballpark with Winzip on speed, and I haven't hit an archive it won't unpack yet.
