Hi,
You might wish to check the following:
- The inputs and outputs have their own gain settings - make sure they are at 0db.
- The inputs can be set to either Mic or Instrument, the latter with variable impedance.
- The output block on the grid also has its own gain settings.
- See this discussion (and posted link) on using TS vs TRS cables on Out 3/4: Do I need to boost +6db when using TS Cable to Power amp?
Output Level set to 0dB is unity gain only when using a TRS. When using a TS you lose half the signal and so a 6dB gain reduction. Note that even if you use a TRS, if at any point you go unbalanced without “compensation”, you will lose gain. So pedals that expect unbalanced ins will typically just drop half of the signal by design (e.g. not make contact with the ring).
Any of these can affect your unity gain.
Hope this helps.
Cheers