Thanks Jeff. System sees it and recognizes it well. Works with iTunes. Just Pro Tools won't work.
In the sense that, I press play and it will shortly try to play back. Then will stop immediately. No sound. Try to setup playback hardware, choose FF400, at times weird sounds and then crashes to desktop.

All I can think of is to check your Pro Tools Aggregate I/O setting in Audio/MIDI setup. If the FF400 works otherwise then this is a PT9 issue.

Is the FF400 selected under the PT device?

Look in Audio/MIDI setup, Audio Devices. Click on Pro Tools Aggregate I/O in the left pane. In the right pane, check "Use" next to RME Fireface 400. Other devices should be deselected.

But it didn't. Actually, when selecting the FF400, both the midi application and pro tools crash to desktop

Looking in the manual, found a way to delete everything about RME and did a clean RME reinstall.
At that point, protools would crash in startup.
Cleaned protools, reinstalled everything from scratch, won't work.
Will have to revert to using the older mbox. Which is a real pity, since the FF400 is way better.

Thanks for your help anyhow,
SD

Fixed it.
Proceeded to downloading the COMBO version of the 10.6.8 update. Avid stated that Pro Tools version 9.0.3 "may not work" properly with the latest Apple OS X update (10.6.8). Recommendation was to use the combo update in lieu of the automatic update.
Once this was done, the crash to desktop was not happening anymore.
Still, ProTools was giving the "audio interface not setup properly" error.

Recommendation from Avid was to start PT by pressin key "n" at the PT splash screen, the proceeding to selecting the proper audio interface from the pop down window.

Done, fixed, works again.