Problem w/ analog outputs from c|24

[CygnusX1]

Hi

I'm running PT HD3 on a Mac Pro through a c|24. I'm trying to set it up so I can use the other 6 outputs ( A 5-6 and 7-8 for example) to send out separate stereo cue mixes using aux sends. The problem I'm having is that I can only send audio through outputs 1-4, When I try to send something through A 5-8 I can see it on the meters of the 192 i/o but I'm getting no audio 5-8 from the "control room out" D-sub cable. I've made all the paths active in the i/o menu. Is there something I'm missing?. A setting inside PT perhaps or some configuration of the c|24?

Also, are there any suggestions for the best way to configure talkback in this situation?

Thanks in advance