Credits: the solution is a direct adaptation of the posting of "nafets" of 2009-04-14 at 22:28 on this page. However, since someone didn't manage to implement the advice, I will give a more detailed version of the same.

nafets points out in an earlier post (2007-10-06, 17:03) on the previous page, that the newer printer drivers won't work, because they insist on interacting with the printer, but the FRITZ!BOX's USB port is strictly one-way only, and thus the computer can't get information about the printer. nafets says that verions 3.0 and 3.1 of the software are ok. Also, in this post he says that one has to download the "AcuLaser CX11N" drivers, and not, as one might guess at that point, the "ActionLaser C1100" drivers!

Note, after you install these drivers, Software Update will eventually ask you if you want to update your Epson Printer Drivers. Do NOT update! The point of this hint is namely to use the old drivers, because only the old drivers work with the WLAN box and this printer!

1. Delete Epson printer drivers from /Library/Printers
2. Reboot
3. Empty trash
4. Download old 3.1 drivers from Epson's US website:
   • Go to www.epson.com
   • Select "North America" -> "USA"
   • Select "Driver & Support" -> "Printers"
   • Click "Laser" and then in the box on the right "Epson AcuLaser CX11N"
   • Under "Drivers & Downloads" click "Macintosh"
   • Click on "Printer Driver c3.1bEs" and then on "Download Now"
   • Make a choice about getting spammed, and click the "Accept" button
5. Double click the downloaded file "epson12208.dmg", and then double click "EPSONLaserPrinter_31bEs.app" and follow the instructions
6. Open "System Preferences" and click on "Print & Fax"
7. Click "+" under the box on the left
8. Protocol: select "HP Jetdirect - Socket"
9. Address: enter "fritz.box" or possibly the IP number of the box, in my case 192.168.178.1
10. Queue: leave this empty
11. Name and Location: you can freely define this to be whatever you want.
12. Print Using: "EPSON AL-C1100"
13. nafets recommends in his/her post to disable printer monitoring, but in Snow Leopard there does not seem to be such an option.
14. Print a test page. You're done!