Synconizing Sound Files during Playback

I'm trying to create a drumbox with multiple looped sound tracks. The user will have the ability to turn on and off sounds (e.g. hi-hat, snare drum, bass drum, etc). I've figured out how to start and stop sounds, loop them, and remove any unwanted delay between loops, but I can't figure out how to synchronize the files to one another. For example, if track 1 is playing and I turn track 2 on, I either want it to wait until track 1 is ready to start the next loop, or for track 2 to start at the position Track 1 is already at, so they are synchronized together.

Any idea how to do this?

Dave