Excellent! Very very interesting, and fwiw, I have had subs in 6 rooms over the last 20 years. Obviously with varying degrees of success...but ultimately, with the X1s and now the XLFs (which are still yet to be set up/calibrated to the system/room)...I have always found that even when severely cut off above 40hz and basically silent through certain passages, they are a must have for me when it comes to that sense of the venue, the spacial cues, the 'enveloping sense of space and realism'...and of course certain music where there actually is a lot of information in that subterranean level. And that is a single DD18+, let alone dual Subsonics...