I would start with a flavorful liquid like chicken stock and some aromatics. After the protein is cooked, season and or thicken the liquid to taste. The liquid will take on some flavor of the protein.

I actually just want to poach the protein at a controlled temperature but use the extra liquid to create a light, yet flavorful nage, that is a perfect portion for each bag.

The purpose of sue vide is to cook the meat the same way as a braise or poach using less liquid then you would traditionally. Put grill marks on the meat, put it in the bag and add flavorful liquid and/or seasonsings and cook until done. Depends on the protein for how long you cook.