Where to locate Equipment?

Whatever works and is convenient.

Anything goes.  You never know what sounds best until you try and hear it. 

It you do not have a turntable it makes no difference sonically where you put your equipment. From a cable perspective, it is best to keep mono amps right behind the speakers keeping the speaker cables as short as possible running balanced cables to the amps. 
You want to keep turntables as far away from the speakers as possible 
Ideally in another room. 
I do not like equipment between the speakers for aesthetic reasons. I do not want to see cables and complexity. My system doubles as a theater so I have a big screen in the middle. The equipment is in a custom built in cabinet to my left side. Seated at the listening position you can not see a single wire. Perfect.

"...From a cable perspective, it is best to keep mono amps right behind the speakers keeping the speaker cables as short as possible running balanced cables to the amps..."

Why is it better to keep high level cables short and low level cables long? 

Its not. But if ever someone says anything once, and it gets repeated, then before you know it everyone is saying it and convinced it must be true because.... someone said it.