Dakkon,
Let me make sure I got this straight. If you unplug the cable from the Marantz, your laptop will grab an IP? Are you *sure* that you're not confusing the IP from the wireless of the laptop? I would turn off the wireless in your laptop and try again.
But make sure you use the cable that's connected to the Marantz. Might as well as kill two birds with one stone.
If your laptop grabs and IP via the Ethernet cable (with wirelss turned off), then plug it back into the Marantz, reboot the AE/Marantz to clear out the ARP table, and see if you can ping the IP address that you assigned to the AVR from your computer.
That is what I did; used the cat 5 cable from the airport express to the laptop, with wireless turned off (to ensure I was connected to the network via ethernet through the airport) just like the marantz would be.
I did not think to ping the static address I assigned the marantz at the time. I could try that.
The link light for the applicable port does light up on the marantz
