Well, before blaming the hardware, I'd make sure that everything is configured correctly. If this is the first time you try to use the network with homebrew, then there might very well be something wrong with your configuration. Connecting homebrew to the PC is not so easy as playing games online. You have to take care of IP settings and make sure that client (PS2Client for host protocol) or server (for samba shares) are running correctly.
If you are familiar with homebrew networking and there surely is nothing wrong with the configuration, then I'd say it's an incompatibility with the new NIC of your PS2. Don't know if that can be fixed, cause EEUG would probably need access to such a PS2 model for troubleshooting and debugging.
best regards Jones23