I tried the Software Updater Upgrade button on the TX1 for 16.04 unsuccessfully.
Done it in 32 bit OS and 64 bit OS.
When booting, 16.04 shows up but:
Last error I got was:
tegra-xhci: failed to init firmware from filesystem: tegra21x_xusb_firmware
Anyone else got 16.04 on your TX1 successfully?