Solved at last! I'm now running apcupsd on a ReadyNAS 1100 with 4.1.6 firmware.
To do this I had to add ssh and root access packages from the Netgear support site. Once I'd ssh'd in as root, then I ran "apt-get update" and "apt-get install apcupsd." Then I configured /etc/apcupsd/apcupsd.conf as appropriate for my setup. Then I started apcupsd by running "/etc/init.d/apcupsd start". That's it -- simple!
The one last step now is to decommission that extra NUT server I'd set up just for this one ReadyNAS device -- all our other stuff runs apcupsd.
