You load patches onto the USB drive in the Preen by holding down the ENG button (top left) when you power it on. Press ENG again and wait a minute for it to connect to your computer (it's slow, just wait). Now you can load the patches onto the USB into the DX7 folder. I loaded a massive number of patch banks into a sub-folder, then moved groups of banks into the DX7 root folder to test them out.
Press a button on the Preen to un-mount the USB, then reboot the Preen by pressing MENU (right lower button).
Now you can MENU, LOAD, BANK, Select-a-Bank, Select-a-Patch and test one out.
Once you get done testing the banks in the DX7 folder, repeat the process to test another set out.