Pro Audio Technology speakers

@txavgut --

The system will be used 50/50 for movies and music. [...] the subs (LFC-15sm) don’t seem especially impressive, claiming response only down to 20Hz. But I realize specs aren’t everything.

If used 50/50 for movies and music a 20Hz hard deck might be a very appropriate compromise. A lower tune affects bass presentation, and while depth-wise it will reveal infrasonic information found on the source material from select Blu-ray and 4K UHD titles, it also has impact on the central to upper bass character and therefor potentially, depending on the chosen cross-over frequency, the integration with the main speakers.

I like crossing over to the mains fairly high (~85Hz), while not least high-passing the main speakers at the same frequency to relieve them from the lower to central bass, which then cleans up their upper bass to lower midrange and adds further headroom. Similarly, if one would, I prefer not to run the midrange/HF horn + compression driver down to their lowest (professionally) recommended cross-over frequency, but just enough above it (with high-order slopes) to clean up the sound bit and aid energy-coherency (that’s the term again - energy coherency: in combination with phase and timing behavior it’s vital for music reproduction to create a smooth sphere or "radiation bubble" of sound in front of you).

Honest 20-ish Hz extension at close to war volume, still effortlessly reproduced, is something that won’t be easily forgotten, and makes sub 20Hz extension that’s any less capably reproduced (i.e.: that takes loads of displacement area, btw.) seem kind of blah and not worth it. Just my $0.02..

If you have the income, give them a listen first. 
May be a bit harsh in the treble.....

@phusis Incredibly helpful and interesting info -- thanks. As I've been learning more, it has become even more apparent that system tuning and configuration is very important, and raw specs are not sufficient to understand a system's overall character.

As @arcticdeth said, I really need to find a way to listen to these. Interesting, several systems that have been recommended to me seem to come with concerns about brightness/harsh treble.

@txavguy --

... Interesting, several systems that have been recommended to me seem to come with concerns about brightness/harsh treble.

Aaand it's a common misconception not only on this forum but audiophilia in general - this notion that speakers comprising compression drivers and waveguides/horns to load them will necessarily or certainly be more inclined to sound shrill, harsh, or other adjectives of similar meaning.

One of the reasons I started becoming more interested in waveguides, horns and compression drivers was to avoid the following: direct radiating dome tweeters. I've heard my bad/badly implemented share of them, and they're the one driver principle in particular that's potentially annoyed the hell out of me. A good compression driver mounted to a fitting horn/waveguide, and there are many examples of that, to my ears sounds less like a "tweeter" and more like a natural extension of the lower frequency spectrum. As such it's more naturally "ignited," effortless and has better substance and energy to its presentation.

Direct radiating dome tweeters by comparison generally sound thinner, more overtly (but unnaturally) detailed, and not least more strained. Indeed, if anything it's dome tweeters that has, to my ears, fitted the "bright/harsh" description most closely (by virtue perhaps of being rather malnourished sounding). 

In short: I wouldn't worry about speakers using quality and well implemented compression drivers and horns/waveguides, on the contrary. 

phusis,
I agree with you.