The Amiga is a 4000D with Cyberstorm MKII 060 and Cybervision 3D with Scandoubler and x-Surf 3c.
You didn't answer Michaels question regarding the V9 firmware of the Deneb. V9 is supposed to fix some DMA problems of the Deneb in combination with a Cybervision 3D. You can find it
here (in the support/updates section).
Also don't forget to remove the pio driver in tridentif you're going to try the dma driver (a bit obvious, but I thought I should mention this).
Edit: Sh!t !!! I need some eyeglasses. Just read you flashed the deneb with v9. Maybe you should email Michael so he can investigate this problem.
Edit2: BTW which version of poseidon are you using? The latest is 4.2 and I believe some improvements were made to the PTP class.