Change default audio output to XAudio2 on Windows

Downmix defaults to disabled on non-Windows OSes, because we don't support non-mono output at the moment

src/libresrc/default_config.json

@@ -332,7 +332,7 @@
 			},
 			"FFmpegSource" : {
 				"Decode Error Handling" : "ignore",
-				"Downmix" : false
+				"Downmix" : true
 			}
 		},
 		"Avisynth" : {

src/libresrc/default_config_win.json

@@ -1,6 +1,13 @@
 {
 	"Audio" : {
-		"Player" : "DirectSound"
+		"Player" : "XAudio2"
+	},
+	"Provider" : {
+		"Audio" : {
+			"FFmpegSource" : {
+				"Downmix" : false
+			}
+		}
 	},
 	"Subtitle" : {
 		"Provider" : "CSRI/xy-vsfilter_aegisub"

src/libresrc/osx/default_config.json

@@ -332,7 +332,7 @@
 			},
 			"FFmpegSource" : {
 				"Decode Error Handling" : "ignore",
-				"Downmix" : false
+				"Downmix" : true
 			}
 		},
 		"Avisynth" : {