Here's a sample dbus xml with multiple output. This is handled just fine using DBUS_INTERFACES in the qt .pro file, but it isn't quite handled using DBUS_ADAPTORS (both undocumented...). I get output like this:
The solution I found online was to use the "-l" argument with qdbusxml2cpp, which would then mean I couldn't use DBUS_ADAPTORS anymore, and I'd have to implement some hack of using system calls in the header, or some other method of generating the cpp files. DBUS_ADAPTORS should be able to handle methods with multiple outputs, or someway to pass in the "-l" argument for that variable.
One other thing to note is that I originally had a custom abstract dbus adaptor which worked just fine with multiple outputs as a workaround to using this variable... In case more people stumble upon this issue and are looking for workarounds that work for them (http://doc.qt.io/qt-5/usingadaptors.html).