The Hollis Audio Labs circle has a lot of information on the dspNexus 2/8 system with user feedback.
That would be a good place to start and ask the questions you have.
The microphone placement depends on the type of speaker being measured. For a box speaker, typically 1 meter or slightly longer on-axis to the tweeter is a place to start for quasi-anechoic measurements for crossover design.
The user manual has the LCD control settings available with the remote or rotary encoder needed for using the measurement mic with programs like REW for speaker and room measurements.
