I need help selecting speakers to cover 600Hz down.

This is for a DJ/listening system in a 30 x 20 ft. basement.
I recently acquired a pair Funktion-One Res 1.5 mid/high horns that play down to 600Hz. I am very happy with their performance.
All I want now is to get the rest of my system up to the quality of their sound. To describe their sound in a few words: Dynamic, natural, rich, effortless.
What would be the best matching mids/bass for them to cover 600Hz and below (best in terms of sound quality and efficiency)?
I've only come across one matching midbass horn: EAW MR102. Any other ideas? Any advice related to my quest would be greatly appreciated.

NOTES: Mixer used Ecler Nuo3, Digital Crossover used is DBX Driverack. Also, I have a pair of 18" open baffle subs that currently cover 50 to 200Hz, and coincidentally can be reused in my new system.

Thanks,
Herman

Hello Herman and welcome to FreeSpeakerPlans.
I couldn't find any DIY PA design that will work up to 600Hz, I found some HIFI projects, but they won't match the efficiency of your Resolution. It is a nice system you have, what 18" driver are used in the open baffle subs?
I have uploaded the Res 1.5 Technical information sheet , looks like a simple design for the 18", maybe acquiring a FK1 18" (if even possible?) and build a similar enclosure would be your best bet....

Thanks for your search. Thanks for the compliment. I use Eminence 18" drivers in the subs. I would think that the FK1 approach is a compromise, running the 18" that high. A real stretch there. Maybe not?
I thought, the possible solution may be to make or get a good, high efficiency midbass horn. Like the old EAW MR102, running it from 150Hz to 600Hz. And keeping my subs.
What do you think?
Herman