A friend of mine made his own cabinet for 3 seas 6.5" speakers and then put the tweets and mids in their own cubes on top of the enclosure, and made some weird exposed crossover boards so he could unplug and replace components at will to change the sound and test different combos, they sounded really good, and he made the enclosure exactly to the volume specs seas suggested and he had everything is separate enclosures...
Heres the problem my ascend 340s cost half of what he paid I had to do no work and sound better..... So if you are not doing it just to create your own design for your own satisfaction it doesn't make sense,,,, their are too many people with actual scientific know how, professional experience and clout, with R&D budgets to compete with...
You want to create your own design, figure out the volume of a 340se enclosure and make them with nice curved cabinets and apply a sweet veneer, then just buy a pair of 340s and install all the parts in your box, thats the grills, crossovers, drivers, cables, ports, plugs and tweets for $500 a pair, all top quality stuff, tested and proven... If you really want to get fancy, make them into towers and install a 10" driver in the base...