You will have to pick a volume unit for bales or whatever group your bale fillTypes are set to (solid by default). As I said before, weight/mass display is secondary to the Farming Simulator games. I added them in as an option (toggle). The reason being is because, some fillTypes either have no mass or have an inaccurate mass (for game physics reasons). Also, some screens display units based on a group of fillTypes, meaning there is really no one mass to calculate off of. That is why, in the vanilla game, everything displays in volumes by default.
So, my suggestion would be to either pick a different volume unit for solid (or your bale fillTypes as I mentioned earlier), or just stick to the bushels and toggle over to weights when handling bales.
If you need help with the setup xml, you can go over to my facebook page and send me a message there.