When I say "sync well in this fashion", I mean it doesn't embed signposts or mark the file in any way, merely stores an offset value and BPM setting in another file. Which doesn't strike me as the most stable way of doing things. So, I dug up a program which extracts BPM settings from a file, accurate to one hundredths of a beat. Without that kind of accuracy, things will start off synchronized but slowly drift apart. So, automating that helped a lot. But finding the offset value is still manual trial-and-error, and more trouble than it's worth. Still, it did everything I hoped for, and the results were rock solid. At least on my computer, which isn't anything close to the target platform.
End Result: One day completely wasted by senseless distraction, and the knowledge that putting in music I've written (and buying a laptop with TV output and two dancepads) would make me very popular at parties.
(Side Thought: Our children probably won't need DJs to work their wedding receptions. That functionality will be built into the hall.)
So, yeah. I hear there was a game or something.