The WiiM App measures your in-room response, calculates 10 Parametric EQ filters to correct the response, then writes those filters to the WiiM.
More info can be found here:
This thread is for discussing your personal experience testing the Room Correction feature that was introduced with v4.8.611162 for the WiiM Pro, v5.0.611253 for the WiiM Amp, v4.8.611251 for the WiiM Pro Plus and any related later beta versions. If you feel you have encountered a bug, please...
forum.wiimhome.com
Room correction uses the default EQ capabilities. Only difference is that the filter values are calculated automatically.
Every WiiM with Sub out (Amp, Amp Pro, Ultra) supports, or will support setting crossover frequency, phase, level, and delay.
Customizing the crossover slope isn't supported yet, but I wouldn't be suprised if it gets added later on.
You can use your iPhone's or iPad's built-in microphone, or an external microphone connected via USB to the WiiM App.
WiiM are also evaluating whether it is feasible to use the WiiM Remote's built-in mic for in-room response measurements.