First of all, thank you all for the input. Eric offered to help (appreciated) but I mostly wanted to see/hear what other people do who are not 'professionals'.
So, I've tried some more. I almost have it figured out, I managed to get the bag underneed the handlebar with the brakelevers in an operational state. Only the shifters rub against the bag, making it hard to shift. The spacers that came with the harness are not sufficient to get the bag low enough under the handlebars.
What I did was take all the cables and strap them to the stem to get them out of harms way, fit the harness with the bag inside and then unstrap the cables. I can see why longer cables would help. Fortunately, I have mechanical disk brakes so that can easily be done but as I only changed all cables recently, I'm a little reluctant to redo that job right now.
So, the setup is in a semi workable state right now.
Things I'll try next:
- find something to add more space between bar and bag so I can make the shifters move more freely. More spacers in the vain of what came with the harness.
- possibly a wider handlebar. My singlespeed with wider handlebar (and no shifters of course) is an easier fit! I have no problems fitting the harness to that bike.
I'll keep you updated. Keep the info/pictures coming. I'm mostly interested in shimano shifter/harness interference (or lack of)!