Yup, it's imperfect. It's not your ROM, it's the status of the emulation. It actually uses the starfield from Galaxian, not the native one from Galaga because they haven't figured it out yet.
Only recently did they figure out the Namco 54xx CPU set, and now Galaga doesn't require samples anymore! But you have to be using .89u6 to get that to work. But it's sweeeeeeeeet.
About the message, the only way to get that out would be to either compile out the messages for *all* games, or change the code for Galaga so it reads as perfect. Your call.
Edit: wouldn't you know it...start typing, walk away for 15 minutes, and there's already a ton of replies.