I am afraid that I can't help you as I do not use a router or wireless but as I have been toying with the idea of converting my network of two pc's at present to wireless and appreciate the benefit of using a router I would have been interested in a solution to your problem.
I wondered if the fact that you are using, in effect, two routers could be a problem. Alternatively, although I can't see a problem in connecting one of your pc's by cable, I wonder if this could cause trouble. Have you tried a wireless connection instead just to see if it changes anything.
Anyway, this will bump your thread up and maybe someone else will be able to help.