Have you tried tip rolling? If not I would definitely try it. I had a similar experience as you with a couple iem’s. I couldn’t get them to sit well or make a proper seal. So I bought a bunch of tips, and found out the Dunu S&S give me the best comfort and seal.
So it’s worth a try. I read all the time about people not liking the tips that came with their iem. Then they’ll tip roll and find the ones that work for them.
As for a stack for iem’s I don’t think that’s needed at all. A simple dongle should do it for most of them out there. That’s half the appeal of iem’s, that they’ll run off a potato.