I had not heard that, although musicology was never my area. A bit of research on Wikipedia (http://en.wikipedia.org/wiki/Chinese_musicology (http://en.wikipedia.org/wiki/Chinese_musicology)) reveals that there were 12 lü (律) -- basically similar to modes. So it wouldn't surprise me if someone at some point had assigned one 律 to each Principal Term. It's exactly the sort of thing that crazy systems people would do, before they had computers to mess around with. :-)