mr816 n12 studio sends c6

I’ve been using C6 and n12 and added mr816 for more inputs.
mr816 phones 1 and 2 are C6 studio 1 and 2 .
I use studio sends to send all n12 and mr816 channels to studio 1.
The only channels I can hear through phones 1 are the inputs plugged
into the mr816.
Sorry… lets go back… this all applies to when we are playing and want
to have separate headphone mixes. We can’t get the channels from the
n12 to play out through the mr816 phone jack , even though in C6 they
are all sent to studio 1.
Am I doing something wrong , or it just won’t do it ?
Otherwise…great setup!

O.K… So I went to VST connections / Studio and added an external input bus,
and set it to N12 L and R.
Then I went to control room mixer / Studio 1 and changed it to
studio source external . Now I can hear a mic (live) plugged into the n12
through studio 1 ( phones 1 on the mr816) but it has huge latency problem.
Anyone have better understanding of this than me?