Hey, Metal Horse, I cannot believe how close your situation is to mine!
I play in a symphonic metal band as well and recently switched to a 6U rack with Kemper and XR12 + in-ears. I have not used a cab for the last three shows and it's working out beautifully!
In my case I connected the headphone out into XR input for the in-ears and FOH gets main out L. This way I get to use Kemper's 'space' feature for easier headphone sound and both headphone out and XR in are in the front of the rack, so a simple pedal patch cable connects them nicely.
I have a question for you about in-ear amplification. I am fully wireless and things are working well but the rest of my band is still wired and I find that when I lower the XR bus out to avoid distortion, the headphone amps they use are not loud enough (https://media.music123.com/is/…4000000000-00-750x750.jpg).
What do you guys use for amplification?