Vibration is a killer of high sound quality.
I am not sure this is true. If you think about it, all towers, including the ultra expensive Wilsons, the Kef Blade etc have the woofers together with the rest of the drivers (albeit sometimes in separate chambers). In fact, the 8c themselves have built in subs in the same cabinets. In these systems, it’s almost impossible to isolate totally the low frequency drivers vibration from the mid-high drivers.
Your second point however is absolutely correct: to optimize placement, the subs should not be in the same location as the monitors.
@ghdprentice