When I got it to work before, I would link the 7zip files with Redream on Launchbox. It showed empty (like normal) after Launchbox extracted (supposedly) the games temporarily for individual plays. From there, I pressed the menu (3 bars) button on my phone which showed the multiple windows open, then I clicked back on the Redream window and it played the game fine.
With whatever update happened in Launchbox in the past year, this trick no longer works. I just want it to work again so I don't have to use Reicast through Retroarch because that crashes a lot of the games.