Miscellaneous
Mackie HM-400 Headphone Amplifier
L/R main stereo inputs plus L/R stereo outputs 3 headphone outputs per channel Aux input on each channel with balance control to mix main and aux signal Mute and stereo/2-ch Mode switches per channel 12 total headphone outputs
https://www.bizrate.co.uk/miscellaneous/mackie-hm-400-headphone-amplifier-oid29503645667.html