Recording with Cross Pack in external mixer mode.

I've had some trouble recording my mixes in Cross and I've realised its because I'm using the external mixer option. I've tried running an rca aux adaptor through one of the outputs on my mixer and then the aux into my laptop (setting Cross to record via aux) but I still get no sound when I record.
What other options are there for recording my mixes? cheers
What other options are there for recording my mixes? cheers