The output of the GBD2 (or whatever is the last pedal in your chain) would attach directly to the input of the DI box.The volume pot on the last pedal in your chain will set the level that goes to the power amp. The power amp probably also has an input level pot, I would think. The same level goes to the XLR output in most DI boxes. That is normally not a concern because the mixer at the studio or HOUSE DESK has an input pad that adjusts the level coming from the DI box. So, I would not think that you need to worry about that.