Internal cable routing

[Dan17]

Does anyone know how easy it is to convert to fully internal cable routing? I have a Trek Emonda ALR5, it is semi internal atm but I like the look of fully, despite making it more difficult for maintenance!

I've seen this FSA headset, anyone know if this is all you need or if anything else is required?

https://www.tradeinn.com/bikeinn/en/fsa-n-69-scr-h...

Many thanks!