Hi guys,
I had a little trouble with this originally so thought I'd post how I got Windows Store games to work (note: I have only done this with Forza Apex as that's the only Windows Store game I have). The reason it's a bit awkward is that there's no obvious path to the .exe file, and when I did eventually find it's location, you can't actually get there without certain admin priveleges higher than a normal primary user (as in you'd probably have to enable the admin account). I wanted to avoid that so came up with this:
TL;DR for Forza Apex:
Open Notepad
Paste the following text into the text document:
start forzamotorsportapex:
NOTE: The colon at the end isn't a typo
Save the text file as a bat somewhere (e.g. start_forza.bat)
Open LaunchBox
Go to Game>Add
For the application path, locate the batch file you created, and fill in the rest of the game details manually (or just search for Forza Motorsport 6 - unfortunately Forza Apex isn't in the DB as far as I can tell)
So this is how I did it, and hopefully it'll work for other Windows Store games too:
Start your game
Start task manager
Find the game in the list of running processes. As it's a game, if you order by CPU or memory usage, it should be near the top
Right click on the game, go to properties
If you're lucky, the "Description" field will say the .exe name (e.g. forzamotorsportapex.exe)
Take that name, and remove the .exe part from the end
Open notepad
Type start, followed by the name you just noted down, followed by a colon, e.g. start forzamotorsportapex:
Save the text file as a batch file (File>Save As>Select a location and call it whatever you want with .bat at the end, e.g. start_forza.bat)
In LaunchBox, go to Game>Add, and fill out the game details, then under "application path", select the batch file you created
Hope this helps some people! I hit the issue and couldn't find any reference to anyone else that has, so hopefully this will help people on the forums and random Googlers. It may be possible to streamline this process or maybe to grab the list of installed windows apps (I know you can do Get-AppxPackage in powershell but it doesn't return the actual app start command - if anyone can figure out how to list possible Windows Store start commands that would likely be very useful for the LaunchBox devs so they can automagically add Windows Store games without having to do this weird workaround).
Anyway, enjoy!