If listening to the Monitor or Phones Out, there are two volume controls available: Digital And Analog. Make sure that the Digital volume has not been attenuated.
With Hilo firmware version 8, there is also now a Master volume control. In Settings > System > Rotary Control Settings, turn Master Out OFF. Warning: this can create a sudden increase in volume, so attenuate outputs before doing this.
If the output levels are low on the Line Outs, check that the Line Out Trims are set appropriately for your monitoring equipment, from Settings > Audio.