Component Stacking Question

Stacking the amp on top is the only way if you must stack. Better off putting each component on a separate shelf, with as much room in between as possible to reduce effects of EMI and restricting airflow. Typically, the power amp needs the most breathing space, followed by the preamp and then tertiary components. Remember, heat is the enemy of electronics. 

these two specific pieces:

I would put a 1" spacer in between them so the pre-amp rear vent could do it's job, then stack away.

Then how do you explain how an integrated amp works? It's all in one chassis in even closer proximity to the low level preamp section, and seemingly sounds ok....I see absolutely no issue in stacking.

Audioguy85 you don’t understand the OP’s question. The whole point is to optimize placement from cooling/airflow and interference perspectives, it’s not not about what is or isn’t possible. 

Stacking is usually done because of space considerations, at least in my case. But if I have to do it, I use a platform/bridge that I have a friend custom-make for me at little cost (usually around $50). Simple but effective. Personally, I would not stack an amp/preamp unless there was no other choice. I'm also a believer of cooling fans for amps in 'dense' installations.