There is a little red INIT button that can be used to reset the system to defaults if held down for about 15 seconds (assuming this has not been disabled from the GUI). This button is located just inside the front door under the display so is not obviously visible.
Another possibility is to remove all the disks in turn, attach them to another system and remove existing partitions. Then when you boot up the system will be in so called 'EM' mode waiting to be re-flashed. It should be possible to do this without knowing the password if you do it in debug mode - and from there select the option to clear the user config. If you are going to consider re-flashing you may want to get telnet enabled firmware from my web site
. The link on how to run firmware updates also includes how to set up the re-flashing software to run in the Debug mode mentioned above.
If you decide not to proceed, then I am always interested in taking the box off your hands (rather than scrapping it) and would pay costs in getting it to me. It would be of use to me even if the disks were first removed.