A REAL iTunes server on NAS I am certainly not the only one dealing with the issue (looking into questions here which deal with some aspects related to an iTunes Server or looking at the Apple Support Forum). So I ask:

What is a way of having a real (explanation of real follows) iTunes Server on a NAS?

Driving force of course is the desire to centralize my iTunes Library, photos, big data, that I do not want to carry around with my me. Solution: A Network Attached Storage (NAS). For all the other stuff except the iTunes library this solution is great. Of course I can put the library on it BUT: 


I will not be able to stream content to my iDevice directly (I could if my Mac is, but not directly)
I cannot tell my library to stream some music to an AirPlay device from my iDevice (again, only if my Mac is on)
In principle: Without any other device(s) running, my library can do nothing. It is not stand alone! To stream content requires additional devices running.


Any NAS that can store any of my data (ok that's every NAS :)) and serves as a stand alone iTunes library I consider a real iTunes Server. I would consider it a real real iTunes Server if I can remote it via Apples Remote App and stream music/videos via Apple appropriate apps  (yes I kinda favor Apples solution whenever available).

I will give myself an answer for one possibility (an additional Mac) with pros and mainly cons. But I am very interested in other solutions (please as well do not hide disadvantages from your proposed solutions)!
One possibility: An additional Mac.

Pros:


Could do everything asked for.


Cons:


Expensive.
Power consuming.
To save some power, one would let it sleep. So everytime one wants to connect to the library, the Mac has to be waked up.
Setup not as easy as NAS.