Would this be the same if im using a mixer please
First you need to get the audio from the playout PC to the Stereo Tool PC. This can be an analogue cable from the output of the playout PC to the input of the processing PC. It could also be digital (audio over IP). Keep in mind that bad cables or cheap sound cards (like onboard sound chips) may cause hums or other types of distortion that then end up in your signal.
On the processing PC FM MPX is generated, which you need to get to your transmitter. Where is the transmitter located and where is your processing PC? If they are close to each other (i.e. the same building), you can use an audio cable directly from the trace alpha to the transmitter. Make sure that the trace alpha is set to 192kHz sampling rate.