Well thanks for a healthy and compendious array of responses !
I luckily have a boring old MBP with an ATI card running Tiger so I don’t think I’ll have any problem. I think the MXO is the product for me. No doubt there will be times when I need the odd bit of digitizing from tape (from archive footage, esp), but I can always get that stuff into the system somehow, even via firewire or by using a camera as a deck or whatever. A hassle but for the amount of times I think it will affect me, not 2500 bucks worth of hassle.
What a pity I don’t have 2 x DVI ports…