I've been using scope for years - but I just cant work this one out & I'm beginning to lose any sanity I have left

I just bought a Behringer ADA8000 and it's great. In my non DAW system I have all Adat inputs working fine and am just using 1 Adat out pair as a monitor for headphones using Asio out to a seperate amp [see pic] in normal mode.

In my DAW system I am using XTC mode and have all the Adat inputs working fine & routing into cubase5 in vst connections.
However when I'm recording vocals with a mic I would like to switch the main mix temporarily to the Adat out pair & amp [as in the other system] so I can use the headphones to monitor the mix and not get interference from the speakers & then switch the main mix back to the pulsar out after.
I just cant seem to find the right way of connecting up the xtcproject so the Adat outs are visible in vst connections. This is what I have at the moment.

Can someone please point out the error I am making ?
Many Thanks
