Hello Karel,

I assume the serge module is not buffered very well, so its input
creates an lowpass together with the output of the A-138.
I suggest the following test.

A-111 -> A-138 -> multiple

connect cubase with the multiple. Check the waveform and the frequency
range.

Then connect the SSG to the multiple too (cubase still connected to the
multiple). Check the waveform and the frequency range again. I assume
there will be a drop in the high frequency range. If yes, blame it to
the SSG.

regards
Florian