Wish we had this system to help you test maybe someone in the forums might have this HP. Not sure where to go from here other then to use a HD and install the trial version on that to see if this works.
You can change to 32bit mode from the Console - enter CTRL + ALT + T then select Boot Options then System Architecture then 32bit mode - save and reboot.
In the DSS build 3511 there is a the ability to switch the either 32 or 64 bit modes. you can use another system to boot the DSS from then change the settings and save them then shutdown and install on the other system.