Stacking

I would think the vibrations transmitted from the sub would have a negative effect on the speakers.  Maybe build some sort of stand to isolate the speaker from sub.

@larryi , I'm using the altec 311/60 & Fostex 925 horns. So I can dial in per say the directions of the horns.

@abnerjack That's the reason of my post.

 Thanks 

Yes, negative effect(s).  Perhaps too numerous and/or unknown to list here.  To include possible instability of a large objects.  Best of luck on a viable solution.

I hear people have been having success in putting their subs behind their listening position. Just a thought.💭 

Thank you for your post.

I think I'll have to buy a bigger home. LOL