I guess this is becoming the "try to make SDL_mixer work" branch

Move InitSubSystem calls into proper places,
don't use AUDIO_S16LSB (bad according to SDL_mixer docs)
Add error checking

src/sdl/i_video.c

@@ -1701,21 +1701,11 @@ void I_StartupGraphics(void)
 	keyboard_started = true;
 
 #if !defined(HAVE_TTF)
-#ifdef _WIN32 // Initialize Audio as well, otherwise Win32's DirectX can not use audio
+	// Previously audio was init here for questionable reasons?
-	if (SDL_InitSubSystem(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0)
-#else //SDL_OpenAudio will do SDL_InitSubSystem(SDL_INIT_AUDIO)
 	if (SDL_InitSubSystem(SDL_INIT_VIDEO) < 0)
-#endif
 	{
-#ifdef _WIN32
+		CONS_Printf(M_GetText("Couldn't initialize SDL's Video System: %s\n"), SDL_GetError());
-		if (SDL_WasInit(SDL_INIT_AUDIO)==0)
+		return;
-			CONS_Printf(M_GetText("Couldn't initialize SDL's Audio System with Video System: %s\n"), SDL_GetError());
-		if (SDL_WasInit(SDL_INIT_VIDEO)==0)
-#endif
-		{
-			CONS_Printf(M_GetText("Couldn't initialize SDL's Video System: %s\n"), SDL_GetError());
-			return;
-		}
 	}
 #endif
 	{

src/sdl/mixer_sound.c

@@ -77,7 +77,16 @@ static INT32 current_track;
 void I_StartupSound(void)
 {
 	I_Assert(!sound_started);
-	sound_started = true;
+
+	// EE inits audio first so we're following along.
+	if (SDL_WasInit(SDL_INIT_AUDIO) == SDL_INIT_AUDIO)
+		CONS_Printf("SDL Audio already started\n");
+	else if (SDL_InitSubSystem(SDL_INIT_AUDIO) < 0)
+	{
+		CONS_Alert(CONS_ERROR, "Error initializing SDL Audio: %s\n", SDL_GetError());
+		// call to start audio failed -- we do not have it
+		return;
+	}
 
 	midimode = false;
 	music = NULL;
@@ -86,19 +95,31 @@ void I_StartupSound(void)
 #if SDL_MIXER_VERSION_ATLEAST(1,2,11)
 	Mix_Init(MIX_INIT_FLAC|MIX_INIT_MOD|MIX_INIT_MP3|MIX_INIT_OGG);
 #endif
-	Mix_OpenAudio(44100, AUDIO_S16LSB, 2, 2048);
+
+	if (Mix_OpenAudio(44100, AUDIO_S16SYS, 2, 2048) < 0)
+	{
+		CONS_Alert(CONS_ERROR, "Error starting SDL_Mixer: %s\n", Mix_GetError());
+		// call to start audio failed -- we do not have it
+		return;
+	}
+
+	sound_started = true;
 	Mix_AllocateChannels(256);
 }
 
 void I_ShutdownSound(void)
 {
-	I_Assert(sound_started);
+	if (!sound_started)
+		return; // not an error condition
 	sound_started = false;
 
 	Mix_CloseAudio();
 #if SDL_MIXER_VERSION_ATLEAST(1,2,11)
 	Mix_Quit();
 #endif
+
+	SDL_QuitSubSystem(SDL_INIT_AUDIO);
+
 #ifdef HAVE_LIBGME
 	if (gme)
 		gme_delete(gme);

src/sdl/sdl_sound.c

@@ -1213,6 +1213,16 @@ void I_StartupSound(void)
 	// Configure sound device
 	CONS_Printf("I_StartupSound:\n");
 
+	// EE inits audio first so we're following along.
+	if (SDL_WasInit(SDL_INIT_AUDIO) == SDL_INIT_AUDIO)
+		CONS_Printf("SDL Audio already started\n");
+	else if (SDL_InitSubSystem(SDL_INIT_AUDIO) < 0)
+	{
+		CONS_Alert(CONS_ERROR, "Error initializing SDL Audio: %s\n", SDL_GetError());
+		// call to start audio failed -- we do not have it
+		return;
+	}
+
 	// Open the audio device
 	if (M_CheckParm ("-freq") && M_IsNextParm())
 	{