same here mate!
i got my hands on a i9505X at work (with sim tray and mmc slot) but i can't deactivate demo (retail) mode. everytime you poweroff the device it wipes every change.
it tried flashed a i9505 stock rom via Odin and it fails in the modem.bin part...
i was sucesslfull at rooting the device, but now my i9505X takes ages to boot (stuck in Samsung Galaxy S4 for a while) and has no wifi
i tried almost every i9050 kernel available with no luck...
Samsung Galaxy S4 GT-I9505
Nokia Lumia 920
Stock Windows Phone 8 (For now...)