It's interesting to know about another option. The PrinceXML dependency sounds like a real pain, though. I'm also not crazy about having to install a bundled version of PHP.
I think if I were writing a book, I'd use TeX. There is a learning curve, but it's very powerful and stable. I know that TeX is used a lot by mathematicians and computer scientists, but I'm not too familiar with how widely used it is in the mainstream publishing industry. Does MS Word still prevail there?