Running multiple instances of aerender.exe

I'm running a local render farm in my studio, with my own deticated software that distributes compositions acros workstations and renders them with aerender.exe. 

Each workstation runs only 1 instance of aerender, when trying to run 2 or 3 on heavy projects the render are super slow and they often crash.

I want to increase the capacity for my renders, and don't want to buy more workstations,Instead I'm in the search for a monster of a server that can handle at least 12 instances of aerender(I know it's possible for small projects, mine are super heavy and complex)

Is it something that anyone here tried ? there is no much documentation around this subject with preformance testing.  

Thanks 

Elad