… and an other question 
Is it a problem / possible with the 74HC00: http://www.ucapps.de/midibox/midi_thru.gif
… to split the Y3 Out and connect it to A1/B1 and A2/B2, so I’ll have 2 additional amplified Thrus at Y1 and Y2?
I don’t have electronic experience at all, everything I know, I learned in this forum. But if I understand it right, is Y3 inverted and corrected again after Y4. So Y1 and Y2 would be in the right “phase” again too. - Did I understand this right?
http://chdist35.distrelec.com/distrelec/dabldich.nsf/0/E28D7D83826CBE5CC1256BFE003DA1BB/$FILE/T03111.pdf (caution: the datasheet shows different pin assignements)
Greets, Roger