Well, maybe it worked for you because you started with XOS1.1 or possibly because you don't have a 1.6 ;-)
In any case, @ Beebs the ISO they distributed wasnt and xiso, just a regular one; toast handles it fine.
As for xisos, a nice utility (CLI, tho there are a few GUI frontends to it; none I like) called extract-xiso that works in OS X, extracts, burns, and even FTPs xisos for you ;-)