What would you recommend? Are there prefabricated hard or soft shell caes for the Pro X? Or is custom made the only way to go?

I think GC sometimes offers Korg factory bags with the Tritons for the same price. Apparently, you can get Korg bags that will fit your board like a glove. If you gig often, then a hard case is a must. You do what you can to protect your gear. If there's no prefab shell for your board, you can get a custom made one for not much more. There are custom shops that claim they can beat any price. It may be worth it to talk to them and see if that can make a case for you.