There is a difference in output volume when changing between Series/Parallel routing (3bd?)
Keep in mind that when you run things in parallel you are also splitting the dry signal in two. This may cause a perceived increase in volume. A good strategy for running presets in parallel is to use them in kill dry mode so no dry signal is present in both algorithms. Use the Program Mix to set the desired amount of dry level in the signal path. There are other strategies. This is a great video to watch to understand how to better use Program Mix and kill dry to your advantage: https://youtu.be/jxWh3LG-MY8