I'm aware that firewire audio is a dead end street, but in my day job I have to deal with a of my theater's Focusrite Sapphire Pro 40. i tried installing and configuring 2.4.1 from mm:libs, but ffado_mixer didn't even start because some internal python module was missing (called ffado.ffadowindow IIRC). Interestingly it turned out that 2.4.3 has just been released a few days ago and installs the missing file and a few more, I'm not sure why 2.4.1 didn't. With this new version I was finally able to make it all work and run jack at low latency on the Sapphire.