Gabi - I think I understand what you are doing, and of course it works, but its not what you think. Its not because you have a midi playing on the keyboard. You are passing audio signals, not midi files, through the keyboard to your speakers. The keyboard is really only acting as a conduit to the speakers. That has nothing to do with MIDI.
MIDI is a set of digital instructions like play the note C, how long, how loud, which voice to select, which effect etc etc. A MIDI file is thousands of these digital instructions and they then have to be processed through a sound module, because there is no audio. The keyboard really plays a midi exactly as if you were actually playing the keyboard and producing these instructions manually.
On your 125, you were connected through the USB port, so in theory you could have been passing a midi to the keyboard. But I doubt you were. You probably have an app on your iPad which is processing the midi and producing an audio signal. Since the speakers on the 125 were internal, the only way to get the audio signal to them was to pass the sound through the keyboard via the USB. That is also exactly what you are doing on the Genos, except now passing it through through the L/R port. But since on the Genos the speakers are external, there is actually no need to pass the audio through the keyboard to get to them. You could equally well connect the iPad directly to them. That is a choice.
Sorry to be so long winded, but I think its good to understand how these things work, and what midi does compared to audio files like MP3s.
I apologise if you already know all this.
Mike