Unfortunately, we only have 1588 boards in a PCI form factor and not PCIe. The only method I know of to obtain more PCI slots we be to use an expansion chassis, but we don't test those with our cards so I couldn't even guarantee that it would work. Sorry there isn't more we can do.
Thanks. Besides expansion chassis, I found expansion boards that use one PCI slot and provide the user with two Slots. I'll try it and see if it works....