Ok soi’m gonna answer myself

To use you iPad as an Fx Box through your soundcard, you’ll need an app called Aum (maybe there’s an equivalent) capable of routing the different signals.

The trick is to acknowledge which inputs/outputs names in Aum correspond to which physical inputs/outputs of your soundcard. (The layers of inputs/software playback/output in Totalmix got me confused. You actually don’t need TotalMix to use your iPad as an Fx Box).

In Aum:

1. You select Input by clicking on the + button. Then hardware input.
Here i am given choice between Usb1 to Usb 12 (or paired). In my case, with the Babyface Pro, Usb3 as an input in Aum refers to Instrument 3 Input on the Babyface.

2. You select and effect to be applied.

3. In output, you select harware ouput. Here you still have a list of Usb ports from 1 to 12 BUT although the name is the same, THEY DON’T REFER TO THE SAME PHYSICAL INPUTS/OUPUTS.
In my case with the Babyface Pro, USB3 refers here to one of the Headphones ouput.

Hope this can be helpful for someone passing by

Sorry if i confused you. I was saying that you don’t need to use Totalmix to do the routing, not that you can’t

In practice i don’t see why it would not work, you’ll see for yourself as i don’t own the Ufx but for me it was simpler to delete Totalmix from the equation to understand how to do the routing.

Once i identified the ins/outs, then why not using Totalmix to do the « listening » routing (what is called « submix » in TotalMix to dose what/how much you wanna hear in headphones, or in main outs, ...).
I was just glad to realize it is possible to use internal routing possibilities of the babyface pro without having to use Totalmix. Then i don’t know if using it at same time than Aum would interfere/take over the routing used in Aum...