Those look pretty great. I really like your cooking setup on the Smokey Joe.
As far as changing the marinade... definitely add some ginger. That's part of the holy trinity of Asian ingredients (soy sauce and garlic being the other two). Otherwise, you can also try replacing some or all of the sugar with pureed Asian pear, and maybe some honey. Add a dash of sesame oil, to give it a more Korean flavor. Use sriracha, or fresh Thai chili peppers for some heat. Instead of regular black pepper, perhaps try some Sichuan pepper (or even dump the pepper entirely). Those will all give you some subtle changes in flavor. But the main elements are the soy, garlic, and ginger, so you're good with those no matter what.