Thank you Bruce! I don't have a calibration file for the Apex220. It came with a calibration printout of the response. It's within 1db to 10khz, then it's about 3db out on up beyond 20khz.
http://www.apexelectronics.com/pdfs/omapex220.pdf
I'm still a bit confused as to the different method of connection when it comes to calibration versus actual measuring. The neutrik input has 2 different gain levels depending on what type of connection is used. Are you saying to use a jumper from the line output to the hi-z input and leave the preamp turned off? Then when I actually measure, use an XLR connection to use phantom power? I don't think I can configure the MIC input as a stereo input. The outputs are stereo however.
I'm sorry, I'm new to this and easily confused.