How easy are these kits to build? I hear these speakers can compete with speakers costing up to $4000.
If you buy the built cabinets it is very straightforward. I installed crossovers, wiring, damping and drivers in less than an afternoon for a colleague.
When It built my father's in England I started with just the drivers and built the crossovers and cabinets and it took about a week.
TL enclosures have more complex carpentry than other enclosures, but not as bad as exponential horns. They are really worth the trouble. If you look at my threads you will see my views on the TL. If you really want uncolored sound these are for you. The TL reinforces the bass of these Exel drivers below 100 Hz 3 db above other alignments.
One other thing, I and others have noticed that subs really muddy things up and spoil things. My colleague used a Carver Sunfire, and results where less than optimal. The reason being the bass is so much better than anything else you likely have heard. If you want to preserve the purity and clarity and want a sub, you will have to design and build a TL sub.
This is not a shortcoming of the Thors, but a demonstration of the shortcomings of everything else. If you match and build a good TL sub of the quality of these Thors, I can assure you, you will have a better speaker system than anything that can be purchased.
These TLs were deigned according to the mathematical model of G.L.Auspurger. I believe his model to be valid.