The vast majority of TiVo upgrade guides require the use of PC, and there are scant resources and programs for the mac, even though OS X is now a BSD based operating system (meaning most basic linux tools work in BSD as well). Over on the TiVo underground, member A@ron asked for help and got little in response. He eventually found software and figured it out, and posted a full guide to TiVo upgrading using a mac as a result.
[PVRblog]
a multi-tasked stream of consciousness or perhaps just emails to myself