scarlet doesnt work wi nuendo4 on osx10,7

hello folks.

i have a friend who want to update its workstation.
he has a nuendo 4 on an old 8cores mac pro (macpro1,1)
he bought a focusrite scarlett interface (18i8)

its system was snow leopard (10,6), but the scarlett is not compatible with 10,6,
as it is said on the focusrite site. It doesn’t work/ and of course i tried. As soon as you plug the interface, the computer kernel panic. If the interface is plugged at boot, it will kernel panic before you land on the desktop.

So we decided to update to 10,7, lion. It’s the last system this computer can handle. 10,8 can’t be installed on this computer.

Nuendo 4,3 works fine with the built in interface on lion. record play… it’s okay.
But when i select the scarlett nothing work. I have set up correctly the vst connections.
I ve noticed when i hit play, no sound but also nothing appears on the vu meter of nuendo. if i get back to the built in interface, sound go out and vu meter are drawn.

So i don’t know what we can do. We can’t buy a new computer; he already owns an overkill other computer wirh another nuendo. We would like to setup this one only for remote and small session.

Of course, he’s a professional composer and user, he owns all the licenses (for 4,3)

So i can’t understand why nuendo and the scarlett don’t work together.

By the way, we looked to update its nuendo from 4,3 to 5ish, but we only found udpate from nuendo2 or 3 to 5
Where is the nuendo 4 to 5 updater ?
perhaps, why not, going to nuendo 6 but im not sure it is compatible with osx lion.
Have you an idea?