Now the more exciting low-tech discovery. Making a picture in picture type "talking head" video where most of the screen is me going through slides, or annotating a PDF score, but with video of me over in the corner. using only quicktime.
end product looks like this: 
Step one: open QuickTime, and choose File --> New movie recording. Make the window small, and shove it up in the corner. don't hit record. That's your talking head box.
Step Two, leave that window alone, not recording anything. The go File --> new screen recording (and make sure the mic is one. Then use PDF instead of powerpoint so you don't have to go full screen. I also queued up my Naxos playlist down in the bottom corner.
Voila--> finished video has the you talking through the slides. I did score annotation this way too, just using mark up/annotation features in Preview. Pretty low tech. You could pull up Sibelius/Finale window instead of the PDF if you were doing voice-leading or whatever.
That's my hack anyway! hope it's perhaps helpful to some others.
