Since I use an insert (Y) cable from the left output only it is much better. Before I used the L & R with TS and TRS cables. Especially using two TRS cables made it really quiet. Note that the outputs are labeled “Left/stereo” and “Right” 
EDIT: I know ‘solution’ this lacks the theoretical base which has to do with balanced & unbalanced cables in conjunction with the Blofeld outputs and mixers/other inputs - cancelling out and phase shifts etc etc. But it works for me getting a decent output in the first place.