This is probably an issue with Bonjour. Try adding the Calibre content server manually as described at the very end of their page (
http://www.ambibma.com/en/custom_calibre.html).
I'm running a Calibre content server on a private server on the net (e. g. *not* on my home network), serving about 5000 ebooks. Loading the catalogue is at least as fast as Stanza did it - a matter of a second or two.