Bookshelf Speakers Sitting On Dual Subs?

What is the end goal you are trying to achieve? Louder over all playback levels, more thump? The 8C’s appear to have a sub out, is it full range or do they have low and high pass filter capabilities? The drivers in the 3070’s appear to be on angled baffles, are you using them in a side firing configuration or a front and back configuration? Are the 3070’s currently in the room now and if yes are you having any issues?

The first potential issue that jumps out to me could be a phase issue. A lot of drivers facing different directions, specially if the 8C’s are run full range. Potentially a lot of different paths for the sound waves from different sources to take on their journey to your listening position could make for some muddy bass.

The another possible issue if the 8C’s are full range is that your subs may not have much to do. According to the 8C’s spec’s they are good down to 30 Hz, not much in recorded music gets that low, not too mention lower.

@sumadoggie 

Can you do it? Sure.  Will you get good sound? Probably not.  Most people set their speakers 3-4 feet from the front wall and have the subs much closer to the wall to avoid getting boomy bass.

All the best.

Scaling back from dedicated room with audiophile rig into a new home with a great room serving multiple uses. The 8c will sit nicely atop the 3070s about a foot from the brick wall in a room which is open to the second floor, the foyer and the kitchen, and rises from about 8’ on one side to about 20’ on the other. The system is going along a rising 8’-20’ wall, firing across a very asymmetric room. This is a compromise system until a dedicated room appears again. DSP in the subs and the 8c will be this room's best friend. The original question was about the stacking aspect of the 8c on the sub really. I believe that D&Ds DSP correction will even take care of the sub’s behavior when the signal is run through the monitors (even though the 3070s have their own optional DSP). The goal is more bottom octave, and fuller dynamics through the space. I have no doubt that the DSP will do its job, my interest was ore concerning the stacking aspect and, honestly, @normb nailed the landing quite succinctly, I’ll bet.

It will sound very good, but it probably won't be optimal.  Try it and let us know your results.

I believe that D&Ds DSP correction will even take care of the sub’s behavior when the signal is run through the monitors (even though the 3070s have their own optional DSP).

This probably is an overly bold assumption.  If the sub is not in an optimal location and / or its performance is not optimized by its own DSP, relying on an external DSP in attempt to optimizing both main and sub simultaneously would possibly lead to a less desirable setting.  I thought a more logical stepwise approach would be to use the sub's DSP to optimze the sub performance first and then use the D&D DSP to optimize both.  But only you know the best.  This is a quite interesting, educational experiment and please update us on the results.