MultiPC setups don't come up as often as you think, and I'm going to say ISBoxer was not really designed with MultiPC in mind. It would require a fair redesign to have the wizard apply a standard multiPC template, which people would then get annoyed at because it didn't do what they wanted.

As for the options being greyed out. Not sure. I've checked a couple of options to see whether I could get the same behaviour, but it is not apparent whether it is a selected option or not. It may be a language thing, if you are not using enUS, then it may be recognising something in the OS settings. Failing that, it would require a bit more digging to figure that out.