Most adapters don't cut it, but Apple's own Lightning to USB 3 Camera Adapter is actually known to work. Not exactly cheap, but you might be able to pick it up used.
Transfer photos and videos to your iPad Pro with Lightning to USB 3 Camera Adapter. Buy online now at apple.com.
www.apple.com
It should.

And the result should be more accurate
if you did import the Dayton Audio calibration file. This is crucial.
With non-boost mode there's no longer a reason to restrict the maximum gain. Simply go full throttle here as well. As I said, the combined gain won't be >0 dB anyway.
Individual channel or stereo can be a difficult decision. Fundamentally, "individual channel" is more powerful and "correct". Depending on the actual interaction of speakers and room you might not get a satisfying match with the target curve in one channel (or impractical gain when not using no-boost mode). In these cases I found stereo to give the better overall result.
You should also try the new variable smoothing setting and see if it returns more pleasing results.