I have spent a fair amount of time researching options for my next speakers and have decided to go with a DIY design using GR Research's kits. I've ordered the NX-Otica with all the crossover component upgrades and have also ordered the flat-packs for the triple 12" servo subs. I haven't ordered the sub drivers and amps yet, but will do so once I get the cabinets built and finished. All in, it will probably cost me about $6K, but from everything I've read and heard, the combination of the NX-Otica and servo subs is competitive with just about anything on the market from a sound quality perspective, although finish quality will not be as nice as many of the $$$ speakers out there.
The NX-Oticas by themselves aren't really full range. They are designed to be used with the servo subs. By themselves, they go down to between 45Hz and 75Hz (-3db pt) depending on the room. In a larger room, where they will sound their best, they don't get as much room gain so roll-off is higher.
These are fairly efficient speakers (93db) so can be used effectively with low power tube and class-A SS amps. But they can also handle a fair amount of power, so they can deliver plenty of dynamics.
The most significant downside is that you have to construct and finish them yourself, but from talking to others that have built these, this isn't that challenging.
The other downside is that, since these are open-baffle speakers, and two cabinets per channel, you need a fair amount of space to achieve optimal sound quality. From what I've read, they should have at least 5-6 feet from the front baffle to the wall behind them, and at least 3-4 feet to the side wall. Fortunately, I have a 17' x 27' dedicated listening room to place them.
Once I get them built and properly set up, I'll post my impressions. In the meantime, check out the NX-Otica build thread on AudioCircle to get an idea of what these are all about.
https://www.audiocircle.com/index.php?topic=143221.0