That's exactly what I'm after! My wife has the cc-RD430DW on her single bike. I'm thinking get another for me, put it on the tandem. Then we both wear and sync to our own individual heart rate monitors. We both would sync to the new speed/cadence sensor. We would mount our head units to our own bars. And the wife could move her head unit between her single bike and the tandem.

But, Cateye said it won't work (one cadence sensor won't sync to the two head units on the tandem). I don't want to buy it if it won't. Sorry to question you, but are you sure?