Bookshelf Speakers Sitting On Dual Subs?

Paul Mc Gowan sez dual subs at the main speakers is fine and preferred.

well then, it's settled... that's the end of discussion then, right?

oh wait, he sells megabuck speakers with giant sub bass modules mounted just below the mains... doh!!!! 🤣😁

important in life to know when someone telling you something is to help you, or...

Do you have any idea how many extra resonances you create in Speakers by wiggling them around on a sub? 
iso stands are rubber and springs and wiggling jiggle

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 

It seems to work for some people.

https://www.audiogon.com/listings/lisb42g0-goldmund-samadhi-full-range

They my shake right off.