Today's left array measurement finds the excessive phase rotation, IR and step response appearing much improved. The phase rotation is about 1/2 of what it was. Do you know what changes were made? The SPL looks like the mic position was changed a little? Even though the measurement is much improved, I believe the issue is still not fully resolved as I would expect the line array to have more like maybe 90° phase rotation from 100-5000 Hz. See charts below.
Is all unnecessary processing in the AVR is turned off? Are you using stereo mode? Do you have a direct mode choice that bypasses all AVR processing? Is the power amp one that has a internal processor and if so, is all unnecessary processing turned off? Is the DCX is handling the XO for the towers and the AVR the SW XO, or is the DCX doing both XOs? EQ is off in all boxes for this testing?
I really wouldn't expect mode selection, XOs or EQ to be related to this issue. A careful check of all the other digital processer options in the chain may find some setting that does.
A cable loopback test from the DCX left mid-woofer output back to the laptop Realtek input could rule out any processing issues concerning the soundcard, AVR or DCX.
No need to answer all these question unless you find an issue. It is just my thinking it case it is helpful in reviewing the setup to look for any anomalies.
The option is to see of this improvement is repeatable and if so just move forward to complete the setup.
I just noticed that the mic input level for this new measurement is greatly higher than the previous one (-9 vs -31 dB). The chart SPL is about the same however. I don't understand how that would happen. Was the sound level of the sweep 20 dB louder this time? If it was 20 db different was one of the traces manually offset to match the other after measuring? The mic calibration file should include the mic sensitivity so there should have been a 20+ dB SPL difference. I don't see how a mic or mic connection problem would cause the IR issue however.
I did not normalize the Impulse and step charts to emphasize the difference in signal level.