Not quite the answer you are looking for, but for what it’s worth:
I have both a Decklink HD and a Cinewave card in the same G5. The Cinewave has both analogue and SDI breakout boxes, and I alternate between using Decklink and Cinewave depending on project. Most of the time this setup works almost flawlessly, but for bandwidth-demanding stuff like HD capture I usually temporarily remove the Cinewave drivers (or vice versa). On FCP startup Cinewave will always warn me about another Quicktime card and driver being present, but still this doesn’t seem to cause much trouble on SDI and DV projects.
Since Cinewave cards are now officially discontinued by Pinnacle, you might be able to pick one up at a very good price. The card still works fine under 10.4 and should remain doing so up until (and perhaps beyond) the next major upgrade of OSX and/or FCP. Decklink cards also play back Cinewave files in realtime with no conversion, so you’ll find the two working together quite well on the same machine.
Amund