Prepare a low poly for XNormal
Low poly model and cage can be done in ZBrush or Maya. If Maya, then edges need to be soften. The model can have either left/right handed tangent space, it doesn't matter. Using left/right handed model baked out different normal maps, however, Unity or HS doesn't seem to care about this (Maya does). So they both work.
Use default XNormal settings for baking normal maps but the UnityTSpace plugin is needed, using Mikk TB won't work. The plugin needs to be the same version as XNormal found here,
https://farfarer.com/blog/2012/06/12/unity3d-tangent-basis-plugin-xnormal/.
After bake, we'll get a typical blue RGB normal map. This map & the low poly model can be tested in Unity - map (import option type=Normal Map), model (import option Normal=import, Tangent=calculate or calculate split tangent). The result in Unity should look perfect, no UV seams.
Converting the normal map to XY HoneySelect normal map
Can be done in mainly 2 ways
1. Import the map in Unity, put in a scene and build the project as a stand alone pc (.exe).
2. Open the map in Photoshop and save as DDS using NVIDIA plugin
From my tests, #1 is not good. Unity will automatically change the map to -Y when we have +Y map and if we have -Y already it remains -Y. I see no option to change this setting so #1 is a no go coz we want +Y map (manually flip Y in photoshop gives almost similar map to a working map but somehow UV seams become apparent in HS). So use #2 with the options below.
Import using SB3UGS
Just do normal texture import. Don't forget the color space needs to be 0. The low poly to be imported can have either left/right handed tangent space and can be triangulated just before import (no need to do that before bake).