That depends greatly on the device. Your device might use a chipset that is already supported in ffado. If so, try firing up ffado and let us know what happens :)
If your device won't come up, then as you suspected, ffado probably doesn't know how to communicate with it yet. Check the device list for its implementation status. Connect the device to your machine's Firewire port(s) and power it up (if needed). Use the gscanbus tool to verify that your machine actually sees your device on the Firewire bus. If the device doesn't show up at all, check that you have the correct options enabled in your kernel to support IEEE1394 (Firewire) operation. If you have Firewire support configured to use kernel modules rather than being compiled into the kernel, make sure all of the necessary modules are loaded. If you use modules, it's a good idea to configure your machine to load those modules automatically during start-up.
Some manufacturers have been very supportive of the ffado development efforts, either by providing hardware for the developers to work with, by providing technical specs and/or Linux drivers to facilitate getting their devices supported in ffado (or both!). Others have not been quite so helpful or responsive.
If your device is indeed not yet supported, but your machine sees the device on the Firewire bus, you can use the bridgeco-downloader application to grab a bunch of information that the developers will need to begin looking into supporting your device. Feel free to post the information you've gathered to the ffado-user mailing list. (ADD MAILING LIST URL)
(ADD MORE DETAIL ABOUT USING THE DOWNLOADER APPLICATION TO GET VENDOR/CHIPSET INFO)