Don't take this the wrong way, but if you are asking for help on a 6th order you shouldn't build one. Only if optimal can there be any gain and it isn't enough to bother to try. Considering your questions no matter who designs it for you I would bet money on a standard ported box yielding better results. Start with the recommended enclosure size in the store. They are tested and good recommendations. See how that fits in your space. Always a good idea to try to plan for the largest option as things can shrink once the build starts.