Actually, the PCI Slot Architecture uses a passive backplane, IIRC, otherwise PCI Towers and Extender cards wouldn't work.

http://www.sharpened.net/helpcenter/answers/increase_pci_slots

I don't have the PCI spec handy, but I was under the impression that addressing info for slots is not dependent on info at the slot signal level.

DC&DftMFH only covers Designing Cards and Drivers for the NuBus/PDS architecture, but the same "book" for PCI Macs is available on one of the developer CD's, IIRC. What's a good/available CD Cataloging utility for 9.2 or 10.4.11? I have one somewhere, but heaven only knows which box it's in!