another streaming client might have the same issues with your router, so this is a question of trial and error.
Another streaming client, however, will definitely not cooperate with iTunes.
IMO you have the following options:
a) buy one or more ethernet cables and run your network wired;
b) try using Windows Media Player or another UPnP server (TVersity, Fuppes, etc., see here
for more) instead of iTunes and see if these work;
c) replace the router by a model known to be compatible with media streaming.