Thx for the solution but I don't think that my soldering skills are enough to do something like this.
Just reached out to Shenzen Audio here in Germany via Amazon and let's see, what solution we find here. To be honest, I don't have any problems with hum with my Topping D10 and the Massdrop THX AAA 789, so it might be that I stick to the D10. Power is plenty enough so I don't need the extra power through balanced connections. (You could now argue that in this case, the volume of the SU8 might be lowered as well but I don't think that I hear the difference between the D10 and SU8)