Isolation question. Monitor on Subwoofer

Just curious...

I have 2 subs, and due to space limits i have been thinking about going with Monitors and putting them on the subwoofers.

Here is my idea, if anyone knows if this will not work please let me know why.

Subwoofer on spikes.
On top of subwoofer either a marble or granite slab. Felt beneath the slab to keep it from scratching the top of the sub.
Monitor speakers coupled on small custom built stands (possibly built to hold sand or leadshot) to achieve the correct height, spikes on the stand which would sit on the granite above the subwoofer

Would this achieve decent isolation between the monitor and subwoofer? I see alot of speakers with built in subwoofers, or other types of speakers with the fullrange box and monitor on top, (GMA Continuims, Watt/puppy, etc)

Thoughts on this from you Coupleing/Isolation Guru's?

Would this do a decent job of isolation or should i look into other methods?