I think it is 8-9, lots of stuff going on. Multiple horn loaded bandpass calculations, you have the issue of where the midrange ports should be placed in order to get proper mid/HF time alignment. Both don't always match up perfectly with simulations so you have some extra fun thrown in there. The general construction/assembly is much more difficult then a regular speaker box. Crossover design can be a little tricky too. Overall much easier to get good results with more conventional approaches.