I can't figure out why emplode decided to store some songs on the 18 and others on the 30.

This is FAQ entry. Please click here.

some albums will have only half the songs available

For this reason, and because there is no function in Emplode to tell which drive the songs are on, I recommend you simply wipe the drive and re-load the music from your PC from scratch. "Dust off and nuke the site from orbit. It's the only way to be sure."

I begged The Guys for a Drive0/Drive1 indicator in Emplode. I tried to explain that it would be very useful in some situations (such as yours), but they didn't see a need for it so they didn't implement it.