iTunes can't handle TC library

Dear all,

I am using iTunes 11 on a new 13" MBP Retina. I came back to my home country after a long time abroad without aproper data storage situation. I got myself a TimeCapsule which acts as WiFi Router and WiFi Storage. On this TC I have copied my whole music collection from another hard drive.

I deleted my messy iTunes library to start new. I directed iTunes in the Preferences to the folder on TC, allowed organising, but not copying for now. When I now (does not matter if 25 or 300) try to move folders into iTunes it will steadily import for the first 10 seconds, after that get extremely slow and eventually abort. The MBP is right next to the TC either connected over WiFi, but same problem exists when connected via Ethernet on this and another MacBookPro

Hence my question - how do I get a rather large library setup in iTunes when it does not seem to handle it? Any workarounds?

Thanks a lot, all the best

Winston