May I suggest that you may be looking at the solution in a backwards / reverse kinda way, by placing such value upon your camera?
Not that (as you say) there's anything inherently 'wrong' with it... But it is somewhat outdated in 2021.
So rather than trying to find a solution that fits THAT camera, by getting firewire cards and needing to use older less well supported software to use that camera...
Perhaps look at it the other way around and get a new compatible camera instead? No doubt your current camera was very high end back in its day, however would a lower end, yet modern camera perhaps give you at least equal results?
Camera tech has moved on immeasurably in the last decade or so. So what is considered 'low end' today, could still deliver a better result than a a camera that was released in 2006/2008 ?
Then you could take advantage of stuff like Davinci Resolve (Free) wouldn't NEED a firewire card and in essence, you would now be competing on a level playing field within your niche... Just a thought...
TL:DR? Perhaps look at updating your camera, instead of trying to find workarounds for 13+ year old tech
