I've been following the various RC threads since I just recently purchased an Ultra and a SVS 3000 Micro to replace an old NHT sub. My main speakers are Sonus Faber Veneres, driven by Emotiva amps. I'm beginning to play with Ultra's RC feature, fed by a Umik-1 and validated/tweaked by REW measurements. So, what I'm working with isn't too different from your set-up, it appears. First, thanks for all the useful posts you (and several others) have provided on this topic. These threads have helped me get up to speed. Second, a friendly LOL at your Freudian? slip referring to the "Moving Magnet Method".
The text in your quoted post above that I've bolded seems to indicate that you're setting a crossover on your sub, itself, rather than utilizing sub management in WiiM. Thus, am I correct to assume that you're doing nothing to attenuate the output of your main speakers below 80Hz? If so, is this being done because you're not worried about relieving your main speakers from the low frequency load or is it being done because you don't think there's any way in the WiiM world to effectively high pass filter your mains while also utilizing the channel-specific PEQs?
Based on my (very) preliminary experiments, it appears that the WiiM app doesn't support the Sub management options
during per-channel RC measurement but that it does not restrict you from using per-channel equalization simultaneously with sub management. If I'm correct here, then isn''t the optimal solution to do the testing/measuring in REW on a per channel basis
but with the sub management turned on in WiiM? Then, just (manually...sigh) feed the REW filter values into one of your custom per-channel PEQ filter groups and apply this custom EQ while also utilizing WiiM's sub management. To me, this seems to involve the same amount of effort you went through with doing your measurements in REW, but with the added advantage of fully leveraging WiiMs sub management capabilities. Am I missing something here? Would appreciate feedback so that I don't waste time (and annoy my wife even more than I usually do with my audio tweaking)!