So you spent $2,000 on the Kemper but don't want to buy a new interface? I'd throw down the $200 for a new interface with line ins or spdif inputs. With the right interface you shouldn't need a reamp box.
Don't hook it up from the kemper out to the hi-z. That's definitely the wrong way. I think the ux1 has line inputs on the back. Hook it into those.