Here are the steps to add the Wave Link Stream Mix to XSplit Broadcaster:

1) Launch XSplit Broadcaster 

2) Click on Tools on the top menu bar

3) From the dropdown select Settings

4) Select the Audio tab

5) In the Microphone drop down menu, select Wave Link Stream (Elgato Wave:3/Wave:1)

6) Uncheck the box next to Silence detection

• This mutes the microphone if low volume or no volume is detected for a certain period of time. This can cause issues when using the Wave Link Stream Mix. 

7) Set the Audio Mixing Sample Rate to 48kHz

8) After all the settings have been set, click on Apply then on OK to close the Settings window.