Low output from Sonic Frontier Line 2 SE Preamp

MY SF Line 2 SE preamp generates very low output sound. if I increase the sound level to my normal listen level, sound is distorted. Even when I plug my headphone, I can hardly listen the sound. Though all functions are working fine. turning on -> show 2 sets of 3 dots -> push standby - go to Mute with volume level 30 & 30 with BAL1 input -> I can choose any inputs. I have to increase volume to 55-60 to hear any sound, but very weak. Any advise on this?