The Garmin Edge 1030 and surely the 530 and 830 to see the data of the Shimano Steps 6100 and 7000 you have to connect EW-100, for E8000 always EW-100 but you have to delete the original display otherwise it won't work. Sorry but I'm using the Google translator.
I do not think it is possible the Shimano sensor should have priority over gps and speed sensor, I used with minimax version u.s.a assistance up to 32 km, I just need such speed and shows the right speed.