By default, the LIO-8 has the monitor outputs set to monitor level (approximately 30 dB down from the nominal level on the 2882). You can change this if your amps are set to getting line-level in by adjusting the level setting in the Monitor Output path. Or just turn the monitor level up.
IIRC, the 2882 and LIO-8 headphones also have different 0 dB level calibration. Just adjust the level to what you want for proper monitoring levels.