When I sell the dspNexus 2/8 I do the customer DSP crossover design. The customer makes measurements in his room for use in the new design. If you can make REW measurements with your existing setup with REW, then those can be used as well. I can discuss this process if needed.
Once the dspNexus 2/8 system is setup, you can use your phantom powered measurement mic, cable, stand and the dspNexus to make the needed frequency response measurements with REW for the new design. Something like the Dayton Audio EMM-6 or Beyerdynamic MM-1 are fine for the measurements with REW as they have calibration data available after purchase. There is a phantom powered mic XLR input on the front panel to make connection and with Measurement mode drives REW.
The dspNexus 2/8 would go between the AVM90 and Orchard Audio amps direct driving the speakers. It would replace the Sublime Acoustics crossover.
The dspNexus 2/8 becomes the 8 channel DAC output to the Orchard Audio amps. The AKM AK4499EX DAC's are excellent DAC's.
If multichannel decoding is needed, the AVM90 decoded stereo analog outputs can feed the inputs on the dspNexus 2/8.
Let me know if you need any other information.