I have always used wood glues for furniture and cabinet work. Since TiteBond III came out, I have used that almost exclusively for woodworking projects. The strength of a joint is not only the result of the glue used, but also the fit of the parts of the joint. Especially with a mortise and tenon joint, whether it's a Domino, generic loose tenon, or traditional mortise and tenon, strength comes from the wood surfaces being bonded together by the glue. Epoxy seems to needlessly make the gluing process more complex when wood glue would work just as well (unless there is something exceptional about the project like, it will be submerged in water). There shouldn't be gaps to fill in a mortise and tenon joint. It should fit snugly and the wood glue will take care of bonding it. I have never had a joint fail using Titebond III as long as it fits together as it should. That is true with pocket hole joints, biscuit joints, and miter joints put together with glue and brads. Recently super glues have come out and are being used regularly for wood, but they will also not fill gaps. My comments are not intended to be critical so I hope it doesn't come across that way, but I am confused why you feel the need to use epoxy.