I have now tested and am using a new to me VST3 plugin called the Reason Rack Plugin:
https://www.reasonstudios.com/en/reason/rack-pluginI am using the Reason Rack inside the Plogue Bidule plugin (I mentioned in an earlier post), as there is a bit of signal routing required and Bidule makes that easy.
I had been searching for a 4th order 4-way linear-phase crossover (often referred to as a frequency splitter) and I found it in a Reason rack extension called 4Dyne:
https://www.reasonstudios.com/shop/rack-extension/4dyne/ More info from the developer here:
http://www.flowerau.com/4dyneMy main loudspeakers are tri-amplified and I have a multi-sub line array so a 4-way crossover is the perfect solution for me. I am using the Dirac plugin for room correction. Dirac outputs play through the DSP crossover networks so the loudspeakers seem conventional to Dirac. The system is configured as 7.0 with the sub array serving all seven channels. The LFE channel is mixed to the sub array and center channel. I used a delay block to match the latency of the 2-way surround crossover to the 4-way mains crossover. The latency is 7ms and can be eliminated if needed by using the Linkwitz-Riley option in 4Dyne.
The Reason Rack extensions are easy to use and they "flip over" for custom signal routing with patch cables.