I think that it’s a UR-RT4 specific issue since the PHONES1 output is hard-wired to Mix 1 L/R:
(Notice the yellow “Mix” & “Cues” buttons at the top.)
Also, here is how I’ve learnt to route a disconnected Cue to PHONES2:
Problem A:
With “Use Phones Channel as Preview Channel” enabled (according to my Control Room setup), I cannot hear preview sounds out of my main speakers or PHONES1.
It only plays through PHONES2!
Note: I disconnected my main output as shown above in order to use Control Room.
Problem B:
With “Use Phones Channel as Preview Channel” disabled, I cannot hear preview sound out of PHONES2 (unless I set it to output Mix 1).
SOLUTION:
ENABLE “Use Phones Channel as Preview Channel” and plug my desk headphones into PHONES2.
This is due my preference of using Control Room’s red knob to set the volume for both monitor speaker sets (Mix 1).
The only caveat is that I would have to keeping swapping PHONE2 jacks from my desk headphones to the other pair of musician’s headphones if I were to turn the knob all the way down to quiet the room for microphone takes (since I have everything set-up in one room).
If anyone has a similar configuration to mine, please let me know if you have figured a workaround.