6 pci slots it is, indeed. (I went and counted.)
And what else, if anything? Special I/O, scsi or the like? I see on my busted 9500 logic board that there are some chips that don't seem to be on the 7500 logic board that I have lying around.
The 9500/9600 has six PCI slots and 512K of level 2 cache soldered to the board. They lack the level 2 cache slot found on the 7x00 and 8x00 machines and they lack the built-in video abilities. Other than that, they are identical. The I/O hardware is identical.
All of the I/O goes through the Grand Central chip which appears as a PCI device to the computer. So there are actually four PCI "slots" on the 7500/7600/8500/8600/7300 machines.
The PCI bus is controlled by the Bandit chip which bridges data from the CPU/memory bus to the PCI bus. The non-9500/9600 machines have one Bandit chip bridging for Grand Central and the three PCI slots. The 9500/9600 have two Bandit chips. The first one does exactly the same job as the single Bandit chip on the 7/85/600 machines. The second Bandit chip bridges for the additional 3 PCI slots.
So each Bandit chip occupies a spot on the CPU/Memory bus. In the non-9500/9600 machines, there is one Bandit chip, plus the video controllers, Control and CHAOS. The Control/CHAOS combo occupies the CPU/Memory bus space which the second Bandit occupies on the 9500/9600, sort of.
Apple originally designed this family of machines to be capable of having four Bandit-style bridges on the CPU/memory bus. So, in theory, they could have built a machine with 12 PCI slots, or one with 9 PCI slot plus built-in video.
Additionally, Bandit is capable of controlling more than three or four PCI devices. The Apple Network Server uses Bandit PCI Bridge chips. It has six PCI slots, one Grand Central, on-board PCI video, and two F&W SCSI busses on the PCI bus, for a total of ten PCI devices on two PCI bridges.
But wait, there's more. In the Apple Network Server, the video, two SCSI busses, Grand Central and first two PCI slots are all on one Bandit chip. So that's actually six PCI devices on one PCI bus.
So with four Bandits and six devices per Bandit, one could theoretically have 24 PCI devices. Unfortunately, problems with bus noise limit one to about 5 PCI slots per bus. One can have ten soldered down devices, because soldered down devices are less noisy and probably have less trace length than cards. So figure each slots counts twice and each soldered down device counts once, and you're limited to a count of eight to ten per Bandit chip.