If you will flash normal firmware on I9505x, odin will stop at flashing modem... Demo units don't have modem hardware, so you need firmware without modem, or just download a pre rooted firmware.
1. Rename it by removing .md5 extension, so you'll have i9505XXXX.tar.
2. Open it with 7-zip, delete NON-HLOS.bin and modem.bin and flash it.
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