Firebox problem with CEP2.1

Hi! I use a Presonus Firebox as my mic interface to CEP2.1.  I am using a Toshiba laptop for the firewire interface. When I tried to record on CEP using the mono track editor, the levels seems limited to -6db on the level meters. It can't go higher than that.  There seems to be some suppression or compression going on although no compressor or limiters were used during the recording.  But when I tried recording a mono track in the multitrack mode, the levels were normal, it could go higher than -6db.  I have also tried it on another laptop with Audition 1.5 and the same problem exist.  Are there some settings I need to adjust?  Thanks.