Bookshelf Speakers Sitting On Dual Subs?

I have a couple excellent subs - Elac Adante 3070 - which have pretty effective DSP.  I'm thinking of buying the Dutch&Dutch 8c (also DSP).  The Elacs are rock solid.  I'm thinking about placing the 8c on IsoAcoustic stands on top of the Elacs so the 8c is even with the front of the Elacs and separated by the Iso stands: running the DSP for the subs and then the 8c.  Any real drawbacks to this set-up?

128x128Ag insider logo xs@2xsumadoggie

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. 


Rule  of thumb selling audio on average  ,you  want the main tweeter level just about at ear level , that being said doesnot always apply

i bought a like new pair of Dynaudio , 3.5  fooor standers and the tweeter is on the bottom,  this iso tech,isotar  tweeters have great expansion I would buy the iso acoustics pucks to put under the speakers for vibration ,this way too it would add 2 inches to the height and should work out well , just keep in mind toe in as needed 

if sitting in the center.

When I think of low frequency vibration damping, I am always thinking high mass (example: thick steel/granite/concrete plate) sandwitched between think damping (rubber has great internal damping) matts (from high density machine/work matts to softer rubber. May use 'spike' technology to further pinpoint vibration energy for easy killing.