At the networking level, the difference between the content server and the wireless device connection is that the content server opens a new connection to calibre for every book. Said another way, the content server uses lots of short-lived connections while the wireless device uses one long-lived connection. All the evidence I have seen says that *something* on your network (in the computer running calibre, in the router, or in the Tab) is force-closing long-open network connections, thereby stopping the wireless device midstream.
I wonder if the problem is on the calibre machine. What antivirus/security suite are you running? Does the problem go away if you don't run it? Now that you have something that works, if you are tired of these experiments I understand.
BTW: the cloud connection also uses short-lived connections so it should also work.