macOS
CamillaDSP cross-platform IIR and FIR engine for crossovers, room correction etc.
JRiver Media Center supports crossovers for Windows, macOS, and Linux with up to 32 channels of DSP. Besides its own filters, it also supports convolution filters from Audiolense, Acourate, RePhase, and DRC with automatic sample rate matching. It supports VST2 and VST3 plugins. For Windows it can be setup as an audio device so all Windows sound is routed through JRiver Media Center's DSP. It can also accept external audio via ASIO for processing.
Kushview
Element acts similarly to a mixing board in a DAW by hosting VST, VST3, AXX, AU plugins with an easily understandable GUI. Within it you can host additional plugins like:
- X-MCFX: multichannel .wav plugin THIS IS THE XO PART
- Sir3: reverb convolution known for zero latency and good updates across OSs. There are free options out there like MConvoltionEZ & XvolverEssential
- TDR Nova: great low latency parametric EQ with compressor/expander. Other free EQ options are MEqualizer, QRange, Marvel GEQ, Toned.
- Voxengo Sound Delay: for setting individual delay for drivers/subs