The workflow for substance designer to create spec and gloss maps should be the same as if creating the sheets in Photoshop. Spec/Gloss and the Metal workflow are mutually exclusive. They do not have a relationship short of what the engine you are using to implement determines which workflow you should use. Unfortunately, I do not have a working knowledge of implementing the SD produced maps into a valve source engine game (e.g., CS:GO), however I would assume that it is no different then if you were creating the textures in Photoshop. Additionally, if you want to save the individual outputs for implementation, you can do that by running the "export outputs" operation in Substance Designer. This operation will save the final outputs as individual files (in your chose file type; e.g., .png) which you may place anywhere, and then reference in your .qc file for implementation into the game. A final into note I would make about SD is that you may set-up the viewport to be aligned with the workflow you require. You may set the materials to spec/gloss OR pbr to approximate (not exact) the final look in-engine. Note that when you bake materials (if any) inside of Substance Designer, or on your outputs, you will need to determine whether to display the materials in OpenGL or DirectX (affects the direction of the z-value channel gradients if I remember correctly). The two workflows are different. The key to understanding the difference is summarized by one of the SD developers here:
" Metal Rough Worfkow
Base Color Raw color with no lighting information. Small amount of ambient occlusion can be baked in if using it for micro-surface occlusion. The color range for dark values should stay within 30-50 RGB. Never have dark values below 30 RGB. The brightest color value should not go above 240 RGB.
Roughness Describes the microsurface of the object. White 1.0 is rough and black 0.0 is smooth. The microsurface if rough can cause the light rays to scatter and make the highlight appear dimmer and more broad. The same amount of light energy is reflected going out as coming into the surface. This map has the most artistic freedom. There is no wrong answers here. This map gives the asset the most character as it truly describes the surface e.g. scratches, fingerprints, smudges, grime etc.
Normal Normal map
Metallic Tells the shader if something is metal or not. Raw Metal = 1.0 white and non metal = 0.0 black. There can be transitional gray values that indicate something covering the raw metal such as dirt.
* With metal/rough, the areas indicated as metal in the metallic map have a corresponding metal reflectance value in the base color map. The metal reflectance value in the base color needs to be a measured real-world value. Transitional areas in the metal map (not raw metal 1.0 white) need to have the metal reflectance value lowered to indicate that its reflectance value is not raw metal.
Also, with metal/rough, you only have control over metal reflectance values. The dielectric values are set to 0.04 or 4% which is most dielectric materials. The dielectric is hard-coded by the shader and you don't need to set it in Substance. Some shaders add a specular control that allows you to change the fresnel reflectance value at 0 degrees.
Specular Glossiness Workflow
Diffuse Raw color with no lighting information. Small amount of ambient occlusion can be baked in if using it for micro-surface occlusion. The color range for dark values should stay within 30-50 RGB. Never have dark values below 30 RGB. The brightest color value should not go above 240 RGB.
Glossiness This map is the inverse of the roughness map. White 1.0 is smooth and 0.0 black is rough. Describes the microsurface of the object. The microsurface if rough can cause the light rays to scatter and make the highlight appear dimmer and more broad. The same amount of light energy is reflected going out as coming into the surface. This map has the most artistic freedom. There is no wrong answers here. This map gives the asset the most character as it truly describes the surface e.g. scratches, fingerprints, smudges, grime etc.
Specular This map contains the reflectance information for both metal and dielectrics (non metal) surfaces. This is a key difference in the metal/rough and spec/gloss workflows. The same rules apply. You need to use measured values for metals and most all dielectrics will fall with the 0.04 - 4% range. If there is dirt on the metal, the reflectance value needs to be lowered as well. However, you can add different values in the specular map for dielectric materials since you have control to author the map.
Normal Normal map "
- Source: https://forum.allegorithmic.com/index.php?topic=3243.0
The PBR workflow I am more familiar with is what is referred to as the "metal" workflow. The Metal workflow has a preset filetype you may use that outputs the following: Diffuse, Normal, Metal, Roughness. You can read more about the metal workflow at the following places: