So are you saying using the iPad is off the table? I read through here but I’m not entirely sure if you’re dead pan on avoiding using the iPad, or if it’s an option. I think both KQ Dixie and BramBos PhaseMaker can load DX7 sysex data (KQ definitely can, unsure about PhaseMaker).
Hardware wise, sorry, I know nothing in this area haha.
Quick edit: Also, if you’re worried about the future of the project and investing in hardware you might not use later, it might be better to just try this out with the iPad first…