rxTools works as expected on 10.4 o3DS. Download the latest version from here:
https://www.omicron.pw/
and follow these steps to update the newly rxTools(backup your OLD rxTools folder inside your SDcard first, just to be sure):
1)Download the latest build from:
https://www.omicron.pw/
2)Unzip it
3)Go to \release\Tools\ and run cdn_firm.py Running the cdn_firm.py script, you will download a folder named "firm" in \release\Tools\ that contains 3 files.
4)Copy the "firm" folder you just downloaded from the script into \release\rxTools\
5)Delete the OLD rxTools in your SDcard(Back it up first)
6)Now copy the NEW rxTools folder(which is in \release\)
7)Paste the copied folder into your SDcard
8)While booting rxTools up, hold the L button
9)It will now install the new rxTools
10)Profit
Edit: the "firm" folder you will download using the cdn_firm.py script, will download the 3 .bin files you need, instead of the firmware.bin file. The firmware.bin file is used only on old rxTools versions. Just follow the guide to update the rxTools and if it doesn't work, paste your old rxTools inside your SDcard. No need to find the firmware.bin file, as you downloaded the needed ones(the 3 .bin files) for the newest rxTools version.