A web page on the UMAX web site covers information on upgrading C500 and C600 computers to Mac OS 8 (Thanks, Andrew Thompson). On the page is the following quote: "UCC has identified a potential hard disk driver issue which can affect owners of all SuperMac C500 and C600 models if they allow the Mac OS 8 installer to update their hard disk driver at the beginning of the Mac OS 8 installation process. Despite Apple's initial claims and optimism, the recently released Drive Setup 1.3.1 does not fix the problem." It goes on to recommend using Drive Setup 1.2.2. (Of course, Apple's position on this is likely to be that Drive Setup is only supported for Apple computers.)
There is also a related UMAX Software Upgrade FAQ page.