I can report success with recognition of the APC BACKUPS ES-650 using the data USB connection to the CS. Parameters appear in the CS interface and give me battery level and expected life. BUT I haven't unplugged the UPS to test the shut-down feature yet...
I have noticed that it seems you need to "re-enable" the UPS each time you disconnect/reconnect, but now that I have everything hooked up and stabilized, that shouldn't happen too often. This may be expected behavior, but don't forget about it.
FWIW the ES-650 reports just over 30 minutes of expected life with the CS-406 attached.
I have the CS-406 running Firmware Version: 2.0.4 - 3.0382