Well... I'm an idiot. It's been such a long time since I've played that game, I forgot there is no underground theme in this game, other than the Pyramid theme. Just checked to make sure, too. Sorry for the confusion, David! I'll be more careful next time to have my facts straight. Let me try my suggestion again:
Just add another melody line to your coin room theme, and everything will sound good to me. Another xylophone, or a vibraphone would work well there, IMO.
Other than that, just keep going! It sounds really good so far!