I stuffed the M5s and the 160 with foam in my main room and cut all speakers to 80Hz. I'm even more close now to not needing Audyssey. I have a very narrow band somewhere down low I need to knock down.
Incidentally, even with the sphincters plugged, the Onk found all my speakers at 40Hz which I find very surprising.
The one flaw I find with many room calibration systems like Audyssey, MPACC, YPAO, etc... is that the measurements are done with one speaker at a time receiving the test tone, even if the system takes measurements in different locations. It is possible the fancy algorithms can predict what the standing wave results will be when all are firing but, as we have all experienced, the results are not always optimal. I think some of the higher end Audyssey and Dirac systems may actually take multiple microphone samples with multiple speakers firing but I don't know for sure as I don't have the budget to own such flagship systems.
What I have concluded is that the calibration systems are capable of determining the frequency a speaker begins to roll-off. In other words, depending on placement, our speakers are "capable" of 40hz sound reproductions. However, it may not do it as well as our subs... In fact, our subs are probably better at reproducing 80hz and below to our ears which is why many recommendations are simply to set all at 80hz.
That said, taking into account all things that will impact sound in your room (windows, walls, tables, kids, speaker placement, wall hangings, etc...) I highly doubt there is a specific configuration but more of a range of optimal performance. In other words, crossover between 50-80hz is likely to be almost imperceptible to your ears.
I LOVE to play around with the settings. It's an addiction. However, I've discovered what seems to work optimal with SACD's isn't my favourite for Ultra HD Blu-Ray movies. And don't get me going with Spotify, the quality of recordings is just all over the map! (OK, I get the same problems when ripping to FLAC, it's almost impossible to set volume levels equally across different recordings :-( ).
All this to say, if you have a capable sub and you use it, let it do the dirty work and let your speakers focus more on the mid and hi ranges.