Install apk
If you got an android-based factory radio (which is the new interface which usually comes with white needle cars) on your TOURX like I do, you can install android apps(apks) by connecting your car to a laptop via a usb cable and use Android debug bridge(adb) to deploy any android apps you want to the radio.
Car side:

    Go to settings-> about
    Click on the version number several times until a message similar to "You have unlocked developer mode!" appears,
    Go back to settings-> developer menu
    Turn developer mode toggle to ON, on the top right side on the screen.
    Enable USB Debugging, and in the following screen click Yes or I agree.
    Disable Verify App installed over USB

After connecting your laptop to the car, go to the folder of adb, put the apps in that folder, and open command prompt/terminal there.
adb install the_app_you_downloaded.apk
To uninstall, you have to know the package name of the app. It is usually contained in the apps file name with the format of com.xxx.xxxx or xxx.xxx.xxx
adb uninstall packagename
(Eg. adb uninstall com.google.gmaps)
Several findings: 
1. The radio runs on Android 5.1, which is already an ancient version of android.
2. The onscreen keyboard won't popup on some of the apps you installed, haven't figured out how to bring it up yet. 
Keyboard in Google maps works!
3. GM removed Google services on their radio. Any apps (netflix, youtube) that relies on Google play services(gms) won't work. However, Google maps doesn't require gms to run, and it works, just doesn't support login to your Google account.
4. You can find apps on apkmirror.com and download the apks there. The variant has to include armeabi-v7a.
5. Browsers like firefox works, but the lack of pop up keyboard makes it not practical to use.
6. Music apps plays normally and supports next song/previous song button control.
7. Games like angry birds and fruit ninja works, using old installation apks.
8. The best use of this I could think about this is maps, games and video playing, you can store video files on a usb drive and install VLC on the head unit to play them.