Hi,
I can straight away see something that may be a problem, Can you see the upstairs wireless from downstairs. If so you getting a complete clash, 1,3,6,9 are all interfering.
The other issue may be associated with firmware, what are the releases, are they different? Is the network all fed from the same DHCP server or different, is it Windows 03, if so you may need to change the DHCP broadcast from Multicast (default) to Unicast.