Cubase AI 5 Input - Output problem

Im working on a OS X, I have a problem with running Vox Tonelab ST Amp Pedal modeller on Cubase AI 5, Tonelab ST works totally fine on Logic Pro, where I can easily set input to Tonelab ST and output to build in output so I can hear and monitor my guitar. However in Cubase AI 5 I have problems, I can’t set separate in and outs, I was trying to work it out in Audio MIDI Setup on Mac, to create Aggregate Device - to combine Tonelab and build-in output but it doesn’t work how it meant to, still in Cubase AI 5 I can’t set build-in output in VST connection. I know that people use Vox Tonelab ST in Cubase without problems, so please help me out, what am I doing wrong?

Thanks in advance!