Agree on quality of the bass.
Not in agreement on $6k price knowing the great deal on the flat pack and the cost of the amps.
If you add up the cost of all the parts and materials (flatpacks, drivers, amps, No-Rez, threaded inserts, spikes, glue, sandpaper, wiring, Neutrik connectors, etc.) plus shipping to get everything to you you are going to be looking at close to $3k. And that is for unfinished cabinets. You still have to finish them. With this in mind, $6k for finished speakers and amp boxes is not even double the cost of materials; $4,800 is very good for having somebody do all the work for you.
Even $6k is a very good deal compared to what speakers of this caliber would cost from a dealer if they had a mainstream headbadge.
Of course, the more of the work you can do yourself, the lower the cost. Such are the rewards of DIY.