There are so many theories on the optimal equalization like free field, diffuse field, the harman curve etc. I'm definitely not an expert, I'm just messing around. What I did was take the mic I already own, which does not have a calibration file (it's a Blue Yeti), put it in stereo mode, and clamped the sz2000 to it with the best seal that could be made (it was actually a decent seal). I was using the 55x pads by the way. Then I checked my mic levels with the sine wave to see if I was putting out db's in a range that bassheads would be listening to. After that I recorded a sine sweep from 10hz to 20,000hz and then I used REW to flatten it out automatically using peak filters and then saved the automatic eq out to txt file and added in my own bassed boost in the 10-40hz range. The result is what you see.
The Yeti mic has a fairly flat frequency response itself, so it should be fairly accurate, but there are so many variables.... Bottom line is that I thought it sounded pretty darn good so I thought I would share.
The DAC/AMP combo may affect the frequency response as well. The variables are never ending it seems.
The DAC/AMP I'm using are the Behringer UMC204HD and the IFI MICRO ICAN SE. I had bought the behringer, odac, and IFI IDAC2 at the same time and did a/b tests and the Behringer and IDAC2 sounded the best (nearly identical) and the Behringer actually does better on jitter tests (see audiosciencereviews on that). I noticed that with the IDAC2 and the Behringer, I could get the bass louder before distortion than I could with the ODAC and definitely more than I could with the onboard sound.
For 80 bucks the little Behringer can't be beat IMO.