Although I have decided against using the line drivers in my final setup I did test the line drivers with the DOUTX board today.
I used the following configuration.
It seems to work just fine (as ilmenator predicted ). I will also test this in combination with the AOUT_NG board but must make some cables to make that happen.
I also tested this configuration without the line drivers, with the DOUTX4 board connected directly to the TPD board. This also worked without problems.
Update soon!