So today I did the following: 

• installed the fans
• installed the bowdens
  • trimmed the bowden of Ch 4 from 48 to 43cm
• heated the hotend and manually extruded the channels.

Ch 7 was the last one that I needed to do and it turned out to be the one to pop out, revealing that the input bowden coupling is merely just a friction fit. It seems like this coupling form over function; it looks nice but, as you can see, won't stick around for the long term. I never knew such a collet existed, but it could be useful if paired with a grub screw.

(Note: SANPrinter also goes by the name SANBrother)