A few things:
The GUI version of ACP commander you found hasn't been updated in nearly a decade, I don't typically recommend using it. You might be able to make it work for your purposes.
I believe for this operation you'll want a full shell rather than just sending individual commands via ACP Commander. When you send commands that way it only waits a few seconds for the output, in this case you'll want a real shell so it will wait for a few hours for dd to run completely.
From the current command line version you can get a full shell as easy as:
java -jar acp_commander.jar -t <device ip address> -o
telnet <device ip address>
Some other sources seem to advocate zeroing out the start *and* the end - is there any value in this? Not sure if this example works or is preferable...
When doing something potentially destructive it is important to understand what you are doing and why at each step. Wiping the start and end of the drive would destroy the boot partition and leave data partition mostly in tact. I believe this is the opposite of what you are trying to do.
I would think the steps you want to follow would be:
1. Get a root shell, (see above)
2. identify the partition containing the data (it's usually mounted as /mnt/disk1 or /mnt/array1 or similar)
mount | grep mnt
3. unmount that volume so that the OS doesn't try to use it while you wipe it
umount /dev/sda6
4. wipe that partition, leaving everything else alone (this will take a while)
dd if=/dev/zero of=/dev/sda6 bs=4k
At this point you could then re-format from the web interface. It might throw some errors since it won't have expected someone to wipe it like that. In that case you can reboot and see if that helps. If it goes into emergency mode you can do a fresh firmware install (probably a good idea anyway if the goal is to wipe the device before selling/etc).