Talkback STAGE<->FOH Setup

Hi all, can somebody help me out please? Maybe this is discussed before, maybe then please sent me a link to the topic.
Question: What is the best setup for Talkback when 2 SQ’s used. SQ-Rack will be (in future :wink:) on stage managing 10 IEM-mixes. From there (with extra Slink card) with tie-lines to SQ5 which is FOH managing.

Whishes:

  • stage-tech can talk to musicians in IEM-mix
  • stage-tech and FOH-tech can talk to eachother
  • FOH-tech can talk to musicians in IEM-mix
  • both using headphone out on desk

I hope some of you can help me out. Til now I am using one SQ5 mixer to do both. (FOH and MONITORING) Which I understand well. But this new coming setup I have not clean in my head yet. (sorry for my poor Englisch)

Thanks!