Choice of wireless router

larsgorm wrote:
....so I cannot store my whole iTunes library on my NAS and afterwards get access to that library on my different Mac´s and PC´s? (That is actually one of the main reasons for me to buy the Ultra 2 in the first place...)

No - iTunes is a single user application just as all the iLife applications are. It does not support multiple iTunes installations accessing the same library stored in a central location (be that on a NAS or elsewhere - this is not a NAS-specific issue). Rather the 'Apple Method' is for each user to have their own library and then share their media with others using features such as Home Sharing. This is for instance how Apple TV accesses media.

If you were careful such that only one of your macs ever had the iTunes library open at a given time, then yes you could do this - but the chances of you making an error and so corrupting the library is very high.

The most common solution is to store the media on the NAS - that consumes the vast majority of space anyway - and then each mac to have its own library locally as it is designed, but accessing the media from the NAS. This does mean of course maintaining multiple libraries separately. There are utilities available that can sync libraries between macs so you may wish to investigate that, but again those are addressing a general limitation of iTunes