This is only a comment, since it seems what you are doing is very complex. I didn't see you mention SDL::Mixer. You can have multiple channels of sound, see Tk Game Sound demo

If you can get SDL::Mixer to work for you, you should be able to incorporate it with Gtk2. You may be able to use the "do 1 loop" trick of Gtk2

Gtk2->main_iteration while Gtk2->events_pending;
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to avoid having to use the Gtk2 Mainloop. You could let the SDL event loop run things, just repeadetly call the Gtk2->main_iteration to keep the gui responsive. As an example with Tk

#!/usr/bin/perl -w
use strict;
use Gtk2;
use Tk;

my $mw = MainWindow->new(-title=>'Tk Window');

Gtk2->init;

my $window = Gtk2::Window->new('toplevel');
$window->set_title('Gtk2 Window');
my $glabel = Gtk2::Label->new("This is a  Gtk2 Label");
$window->add($glabel);
$window->show_all;

my $tktimer = $mw->repeat(10, sub{
   Gtk2->main_iteration while Gtk2->events_pending;
  });


$mw->Button(-text=>'     Quit     ',
       -command => sub{exit}
        )->pack();

MainLoop;
__END__
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As far as threads go, the recent versions of Gtk2 have a way to share Gtk2 objects across threads, but it is tricky and not generally gauranteed to always work. It has an enter and leave method, to tell Gtk2 to enter and leave the thread.

use Gtk2 qw/-init -threads-init/;

die "Glib::Object thread safetly failed"
        unless Glib::Object->set_threadsafe (TRUE);

.....
.....

sub thread_work{
     
      Gtk2::Gdk::Threads->enter;
        .........  
        .........
      Gtk2::Gdk::Threads->leave;
        
}
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