Are you sure that you aren't clipping during the recording?
Check the track levels and the master level for any clipping (going over 0db).
If the master level is clipping, but the tracks aren't, you are in good shape. Just pull down the track faders until the master no longer clips.
As you add more tracks, their levels are summed together at the master resulting in higher volume and possible clipping.
You could just pull down the master, but I prefer to just leave it at 0db and adjust the mix level via the track faders.
If the tracks themselves are clipping .... you need to re-record them and adjust the levels going into the Firestation, as you could be clipping at the converters but by monitoring off of the Firestation you may not be hearing it while you record.
HTH
-Ken