Any reason why you're not getting rid of the modem/router altogether and just letting the core handle everything i.e. plug internet straight into the core? Then use the second NIC in the core for your internal network. Then no manual setup/configuration will be required.
My ISP gives a black block modem/router that you can't really mess with. The physical location of where the DSL comes into the house vs where the Core/Hybrid is another issue (the house is wired oddly, and would require the modem->hybrid run go across the house, then across the house again to get to the rest of the rooms, cinderblock is not fun to drill through). Its a dumb setup, and I dislike the ISP for it, but the ISP is cheap and works decently otherwise.
More to the point though, there does not appear to be any problems with the network at this time. The Core's DHCP server has taken over, PXE boot will find the core, get the correct information (including where the Core is and the seperate gateway) but it is still timing out. I can successfully manually mount a samba share to the directory tree, but the Core seems to occasionally disconnect it, OR cannot retrieve a directory listing through the media pane.
While I understand that I am using a non-standard setup, all but the gateway value are options you can tweak in the Core's own setup, and shouldn't really be a block to anyone. This is a linux based solution afterall. So how about if I just ask some more specific questions:
Is there a default setup when creating a boot disk that does not accurately get information from the DHCP server's config file from the Core? Where could I find this file? Would that be a possible cause of an incorrect timeout?
Some of the sites for the software updates and modules are very very finicky, would missing one or two archives when running the create image script not only be ignored, but also create a faulty image?
Can we hope for the addition of a gateway field in the web admin for advanced network setup?
Hopefully asking for more specific answers may yield better responses.