I could not resist to contact the Heeresgeschichliche Museum in Vienna if there is something known about the remains of the first Farman biplane built by Voisin.
I just got a response today.
The question is asked sometimes.
I've been told it might be possible the aircraft went in the inventary before World War One, only there are no documents about. And also the biplane is not stored anywhere in the archieves of the HGM. It has been reorganised after WW2 and there was found nothing.
Unfortunately no good news just you didn't need to dig deeper in the basements of the HGM.
Cheers
Aquilius