connect system capture 1 / microphone -> playback 3 & 4 / headphones

snap.xml

@@ -8,6 +8,10 @@
 </alsa>
 <jack>
   <client name="system">
+    <port name="capture_1">
+      <connection port="system:playback_3" />
+      <connection port="system:playback_4" />
+    </port>
     <port name="capture_2">
       <connection port="GxAmplifier-X:in" />
       <connection port="GxTuner:in" />