The PB1400 is NuBus architecture, despite the lack of (conventional) physical NuBus slots, not PCI. NewerTech's G3 accelerators reveal this in the names of their Extension and Control panel: NUpowr. The latest Crescendo extension from Sonnet will inevitably be for PCI Macs, so I suspect that you will need to hunt down and install an earlier Sonnet Crescendo extension. I cannot tell you its version number because all of my Macs (but a DA and an MDD) are still packed after a recent removal to another house. Nonetheless, good hunting.
de