Just wanted to praise Sigil - I've had trouble with HarryT's Omnibus volumes' toc working on my Bebook. I've found that fixing the tocs with Sigil is pretty simple with the help obtained by Valloric and AnemicOak. Lack of a search and replace makes it just a bit more complicated but it's easy to cut and paste from Sigil to Notepad++, add the format tags to what needs to be in the toc, and paste back to Sigil.
The result is a toc, designed just as I want, for the omnibus volume that works perfectly with Bebook! Sigil is really a great advance for epubs!