Dante Controller and "Pro-Tools-First" Issue

[TheNeverknow]

Hello, everyone;
I´m trying to route Channel´s outputs on Pro-Tools-First.
After making the first assignment, (Routing to the 1-2 Dante TX), the other Dante TX channels 3-4 , 5-6 and 7-8 just turn themselves unavailable.

Is it a limitation of Pro-Tools-First? Or is it possible for me to use the other TX Dante channels?

Thanks a lot;
Marco