So, apparently I'm one of almost no one who uses 2 DT amps with my POD HD 500X. I use it to support stereo out primarily, with 2 of the same amp model for the most part. I do have a few patches that use 2 different amp models (the AC30 with the Bassman is a great combination). So, my list, by priority, would be as follows.
1. Configure the proper power amp configuration for the chosen pre-amp(s), for both left and right, while bypassing the DT pre-amp(s).
2. Separate left and right audio paths.
3. Ability to adjust tone, volume, etc. from either the DT or the Helix.
That's pretty much it.