My english is not perfect, but I will try....
Di2 wiring is completely inside the frameset - but the hole under BB area is little bit bigger (about 1cm bigger) - just to get it inside. No contact with crank spindle - because of plastic roller. The biggest problem was cable from RD. The holes inside the chainstays are little bit smaller than end of the cable. I cut it (probably 2mm were enough)
Grommets are original from BH.
Btw. I am going to rebuild it with DA 9070 and this DA electronic kit is for sale
No worries..ur english is perfectly fine and thank you for the explanation. Yes, all the wiring is inside the frame. What i did first was to run the cables inside the BB shell itself. As I was worried that the cables will come into contact with the crank spindle, I decided to run the cables like you did, through that gap underneath the BB shell itself. The routing however is actually meant for mechanical groupsets. Still not happy, managed to find a BB386 to shimano converter from Hope that has a cone in between the bearing cups. The BB cups that came with my frame didnt have the cone.
I think the original grommets are meant for the newer Di2 that uses Etube. It wasnt easy to fit them and I had to resort to melting them slightly so that they would fit perfectly.
The latest 9070 DA would be perfect...but it will burn a super duper big hole in my pocket :p