I went through some methods for how to boot the seL4 kernel on a stock TX1 board yesterday and wrote this guide: https://wiki.sel4.systems/Hardware/jetsontx1

It goes through the steps for getting seL4 booted using an SD Card, the internal 15GiB mass storage on the TX1, or using a USB cable and the DFU protocol. DFU is probably a lot faster/better for you f you're doing active development. Could you try one of these methods and let me know if any of them works for you?

Kofi Doku Atuah
Kernel engineer
DATA61 | CSIRO