It is a pity that there is no good online documentation for Juce.
This comment comes up all the time here, and I don't know what to tell you. When I first started using JUCE, I was like, "wow, an open source project that actually has documentation!" I was literally blown away at how many comments were in the header files.
Yes, Qt has good documentation, but reading the JUCE source has many advantages. The entire source is imported and compiled as part of every project, so it's easy to step debug to find problems; you'll eventually get hit by a jassert() that will help you correct a programming mistake. It's easy to find declarations/definitions of anything in the juce namespace by using your IDE (F12 in Visual Studio, F3 in Eclipse, F2 in QtCreator, etc). A lot of the craziness in Qt like the signals and slots mechanism (and the effing Meta Object Compiler) can make debugging difficult; JUCE is just C++. Good variable names and coding style make reading the source fairly straightforward.
Sounds like you've got some solid dev skills; don't let the documentation thing scare you away.