The frame arrived today! After looking at the spacers, I realized that what I was trying to do isn't possible at all (which is probably why no one replied).

The integrated spacers are much wider than the steerer tube to make room for internal cables, leaving no space on top of the headset cover to route two cables externally. Alternatively, if I use standard round spacers, there is room on the cover for external entry, but no way to route anything internally through the handlebar/stem. As you can see, you've got a newbie at work here!

So, let me reframe my question: For those of you in this thread who have already built a 2x setup, have you noticed any degradation in shifting performance due to running four cables internally with those tight bends?

As for semi-internal routing: my frame didn't come with a headset cap for semi-internal entry. What would you recommend instead? Would something like the FSA No.69 SRS work?

If I go with the FSA, I understand I'll need to swap the bearings since the FSA ones aren't 45°/45°. Does this headset include rubber grommets to prevent water ingress through the ports? Also, would I need to use a different compression ring than the one supplied with the frame?

Thanks again for any insights!