Xboxdrv

xboxdrv is a GNU/Linux driver for Xinput controllers. It can be used to enable simultaneous use of Analog Stick and D-Pad on TheXTech and NSMBX by running the following command:

sudo xboxdrv --detach-kernel-driver --axismap -y1=dpad_y,x1=dpad_x

The reverse also works in SMBX-38A:

sudo xboxdrv --detach-kernel-driver --axismap -dpad_y=y1,dpad_x=x1

Closing the terminal should reactivate the default xpad driver.

Installation
On Ubuntu and Linux Mint xboxdrv can be installed by typing:

sudo apt install xboxdrv

sudoers.d
It is possible to disable the password requirement by running:

sudo visudo /etc/sudoers.d/xboxdrv

And adding the following line:

user ALL=(ALL) NOPASSWD: /usr/bin/xboxdrv

Replace "user" with your username and save.

Xboxdrv.desktop
To make things convenient, you can create a Desktop launcher by opening a text editor, entering the following contents:

[Desktop Entry] Type=Application Name=xboxdrv-launcher Icon=applications-games-symbolic Exec=sudo xboxdrv --detach-kernel-driver --axismap -y1=dpad_y,x1=dpad_x Terminal=true Categories=Game Name[en_US]=Xboxdrv

And saving it as "Xboxdrv.desktop" in the same folder as your game executable.

Links

 * https://pingus.seul.org/~grumbel/xboxdrv/xboxdrv.html