Yeah, that's a good suggestion, and it's something I'd considered (not that specific chip, maybe, but a 20-port I/O expander). But it makes the Arduino do all the work of syncing the displays and updating everything. I'm running 39 separate displays (15 dual 7-segment, 9 single 16-segment), plus a couple standalone LEDs, from the same Arduino... I need to offload the multiplexing as much as possible.