I'm currently in the middle of building up my S-Works Roubaix with R8050 Di2 however the project has stalled as I cant decide on what junction box to use.
I have the 3 port junction that is usually fitted under the stem and have wired the cables internally in the handlebars for that set up but before I put everything together and tape up the bars, I'm mulling over whether I should go with some of the other options, which are:
XT SC-M800 display/junction: This has the added advantage of also being BLE/ANT+ enabled meaning I could program the hidden shifter buttons for additional functions (haven't decided what yet though) This option doesn't require any extra wiring and I'd simply use the already installed wiring)
Bar end junction which would mean buying another Di2 wire and WU111 Bluetooth unit (and the bar end junction itself) and is a very neat and tidy job as everything is internal (more or less).
Keep the 3 port junction and get the WU111 Bluetooth unit and fit it in the seatpost (one extra short wire required) . This is the cheapest option.
I like the idea of the M800 display unit as it has built in BLE/ANT and also it shows battery life in a % figure as opposed to a flashing/vague light, it also shows clearly which shift mode i'm in and finally but of least importance, it shows which cog on the rear and FD position the chain is in.