1) I use the first Routing on the list of the menu routing page,that is A-B with 50% of Level on both    DSPs

2) in DSP B there is No preset, it's in THRU 

3) no,it's doesn't happen with all preset,for instance,all the presets of the Bank #66 Virtual Racks,work fine

4) I don't remeber it,but yes it's very probabile that it happens with the TRHU too

5) Yes,I've tried to swap the cable/amps,but without results,thus the problem move itself to left or to  right

6) yes,my bass is mono.I use an M -AUDIO sound card like a preamp for my bass.I run my instrument into one of the inputs of the M-AUDIO and then the signal comes out from out 1 and out 2 of the sound card,to go directly into the inputs of the H8000FW