If you have a Midi part for your "Audio", which is on another track.Then you go to > Device > Master effects > SteinBergVoice Mac...choose Processor> click the button- in the upper left of the project window to the right side of your Midi channel (example 01 > come straight down to Outit is under- In) > click arrow > you will see all activated out...vst´s etc. >Choose steinberg voice mac >NOW,you need to select the Audio-channel that you want to play with the voice mac.
If you want to play midi to an exsisting vocal track...> Choose Generator and follow the same thing.