The Bowden tubes connect your ACE units to the rear inputs of the Snapmaker U1, exactly as shown in the title illustration above.
Connect slot 1 of every ACE Pro you use to HEAD 1, slot 2 to HEAD 2, and so on.
Recommended: use splitters
On an AMS you could connect everything directly, but I recommend using splitters, joined to the printer inputs with a short piece of Bowden tube.
I recommend this newer Bambu Lab model. I often had problems with the previous version.
Running fewer than 4 ACE units
With fewer than 4 ACE units you can route the original feeders through the same splitters, so you do not have to re-plug anything when switching back to normal mode.
Alternatively, plug a short open piece of PTFE tube into a free input, for example to print soft TPU in parallel. My TPU spool holder works well for this, and a dry box is handy for longer prints.
TPU spool holder on MakerWorld ↗
Removing the original spool holders
If you want to remove the original spool holders, I also have covers for the mounting holes on MakerWorld.