In the Connector Settings wich Midi Ports have you selected ?

Page 47 user manual UFX lll :
These ports can be accessed under the name UFX III MADI Optical and UFX III MADI coaxial or UFX III MIDI Port 3 and 4.

The Midi ports you have to select in the Connector settings therefore shall be : UFX III MADI Optical (input and output)

Thanks Waedi and Ramses for your quick answers. Very efficient and reliable.
So I downloaded the 1.97 beta version of TM with the possibilitiy to include the 12 mic : awesome ! Matthias Carstens is really a master and very caring about his passionnate and professionnal customers.

So I tested the 12 mic and TM. It is to be noted that the gain changes onto the TM main computer screen are directly mirrored on the little 12mic screen but not the reverse : if you change the gain on the unit itself it does not come mirrored on TM.

The main issue though is that only the first 8 mic preamps work like a charm. The others are not recognized. Plus when I go to Options, then SETTINGS, it doesn't matter what I set in there, it is not taken into account, it keeps coming back the ADAT ports. But still the first eight MADI preamps work like a charm.
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Well to sum up this night : I am very happy to have sent my first message and very happy to receive nice feedback and help, thanks again. I confess the 12 mic is little bit confusing for me this is my first MADI experience.

So new questions : do you have any idea how to tackle the "SETTINGS" situation ? Does it come from my setup ? And how to tackle the 9-12 extra 4 preamps within TM ?

Thousand thanks !

Take another look at the screenshots, that's why I made them for you.

My channel distribution on the MADI BUS, related to the screenshots above...
ch 01..08 = Octamic XTC
ch 09..16 = 12Mic Port 1-8
ch 17..20 = 12Mic Port 9-12

Assumed now channels 1..12 for your 12Mic., see below.
It depends on how you have configured the routing on the 12Mic regarding its mic channels from/to MADI Bus (ch 1..64).

General info: since the device no longer corresponds to the 8-port scheme of the Octamic XTC, RME had to come up with something new. The idea here is to enter the 12Mic in groups of 4 ports to support Mic preamps with 4, 8 and 12 Ports.

12Mic Port 1-4:   MADI channel 1..4
12Mic Port 5-8:   MADI channel 5..8
12Mic Port 9-12: MADI channel 9..12

This is what you have to configure now under TM FX -> Options -> Settings (F3), Tab “Aux. Device” tab

Select the Channels (Bank, 8 ports) and enter the ports of your 12Mic under Device 1 and Device 2 in groups of 4.
Device ID, this is the MADI ID of your device, most likely 1 if you have 1 device.
Set MIDI In and Out to UFX III Midi Port 3 (this is MADI optical).

Channels "MADI 1-8":
   Device Type: 12Mic 1-4, Device ID: 1, MIDI In + Out: UFX III Midi Port 3
   Device Type: 12Mic 5-8, Device ID: 1, MIDI In + Out: UFX III Midi Port 3
Channels "MADI 9-16":
   Device Type: 12Mic 9-12, Device ID: 1, MIDI In + Out: UFX III Midi Port 3
   Device Type: None