Still not the solution. The lights go on full white and stay on--they don't execute properly. At the same time (and this is promising because it shows there's a bit of SPI sharing happening) I get a split-second burst of the mp3. Then the lights just hang around on. I pulled this from the developer's board and was wondering if it might have an impact? Not sure how to implement if it is.
"Noting spi.transfer() is also called by refill from an interrupt and hence it needs to be interlocked with the interrupts by surrounding it: e.i."
MP3player.pauseDataStream();
bar = SPI.transfer(foo);
MP3player.resumeDataStream();